Intel storage systems. Differences between SAN and NAS

In the matter of knowledge, SAN encountered a certain obstacle - the inaccessibility of basic information. When it comes to studying other infrastructure products that you have encountered, it is easier - there are trial versions of the software, the ability to install them on a virtual machine, there are a bunch of textbooks, reference guides and blogs on the topic. Cisco and Microsoft produce very high-quality textbooks, MS has at least cleaned up its hellish attic called technet, even there is a book on VMware, albeit only one (and even in Russian!), and with an efficiency of about 100%. Already on the data storage devices themselves, you can get information from seminars, marketing events and documents, forums. On the storage network there is silence and the dead stand with scythes. I found two textbooks, but didn’t dare buy them. This is "Storage Area Networks For Dummies" (there is such a thing, it turns out. Very inquisitive English-speaking "dummies" in target audience, apparently) for one and a half thousand rubles and "Distributed Storage Networks: Architecture, Protocols and Management" - looks more reliable, but 8200 rubles with a 40% discount. Along with this book, Ozon also recommends the book “The Art of Bricklaying.”

I don’t know what to advise a person who decides to learn at least the theory of organizing a data storage network from scratch. As practice has shown, even expensive courses can yield zero results. People in relation to SAN are divided into three categories: those who do not know what it is, those who know that such a phenomenon simply exists, and those who, when asked “why make two or more factories in a storage network,” look with such bewilderment, as if they were asked something like “why does a square need four corners?”

I’ll try to fill the gap that I was missing - describe the base and describe it simply. I will consider a SAN based on its classic protocol - Fiber Channel.

So, SAN - Storage Area Network- designed to consolidate server disk space on specially dedicated disk storage. The bottom line is that this way disk resources are used more economically, are easier to manage and have better performance. And in matters of virtualization and clustering, when several servers need access to one disk space, such data storage systems are generally irreplaceable.

By the way, due to the translation into Russian, some confusion arises in SAN terminologies. SAN in translation means “data storage network” - storage system. However, classically in Russia, storage means the term “data storage system,” that is, a disk array ( Storage Array), which in turn consists of a Control block ( Storage Processor, Storage Controller) and disk shelves ( Disk Enclosure). However, in the original the Storage Array is only a part of the SAN, although sometimes the most significant one. In Russia we get that the storage system (data storage system) is part of the storage network (data storage network). Therefore, storage devices are usually called storage systems, and the storage network is SAN (and confused with “Sun”, but this is trivial).

Components and Terms

1. Nodes, nodes

• Disk arrays (data storage systems) - storage (targets)
• Servers are consumers of disk resources (initiators).

2. Network infrastructure

• Switches (and routers in complex and distributed systems)
• Cables

Peculiarities

For a SAN, the key parameters are not only performance, but also reliability. After all, if the database server loses its network for a couple of seconds (or even minutes), it will be unpleasant, but you can survive. And if at the same time the hard drive with the database or OS falls off, the effect will be much more serious. Therefore, all SAN components are usually duplicated - ports in storage devices and servers, switches, links between switches, etc. key feature SAN, compared to LAN, is duplication at the level of the entire infrastructure of network devices - factories.

Factory (fabric- which actually translates from English as fabric, because... the term symbolizes the intertwined connection diagram of network and end devices, but the term has already been established) - a set of switches connected to each other by inter-switch links ( ISL - InterSwitch Link).

Highly reliable SANs necessarily include two (and sometimes more) fabrics, since the fabric itself is a single point of failure. Those who have ever observed the consequences of a ring in the network or a deft movement of the keyboard that puts a kernel or distribution switch into a coma with unsuccessful firmware or command understand what we are talking about.

Factories can have an identical (mirror) topology or be different. For example, one fabric may consist of four switches, and another - of one, and only highly critical nodes can be connected to it.

Topology

Cascade- switches are connected in series. If there are more than two, then it is unreliable and unproductive.

Ring- closed cascade. It is more reliable than a simple cascade, although with a large number of participants (more than 4), performance will suffer. And a single failure of the ISL or one of the switches turns the circuit into a cascade with all the consequences.

mesh). Happens Full Mesh- when each switch connects to each. Characterized by high reliability, performance and price. The number of ports required for interswitch communications grows exponentially with the addition of each new switch to the circuit. With a certain configuration, there will simply be no ports left for nodes - everyone will be occupied by ISL. Partial Mesh- any chaotic association of switches.

Center/periphery (Core/Edge)- close to the classic LAN topology, but without a distribution layer. Often, storage is connected to Core switches, and servers are connected to Edge. Although an additional layer (tier) of Edge switches can be allocated for storage. Also, both storage and servers can be connected to one switch to improve performance and reduce response time (this is called localization). This topology is characterized by good scalability and manageability.

Zoning (zoning, zoning)

• the selected pairs are added to the zones previously created on the switch;
• zones are placed in zone sets (zone set, zone config) created there;
• zone sets are activated in the fabric.

For an initial post on the topic of SAN, I think that’s enough. I apologize for the varied pictures - I don’t have the opportunity to draw them myself at work yet, and I don’t have time at home. There was an idea to draw it on paper and take a photograph, but I decided that it was better this way.

Finally, as a postscript, I will list Basic guidelines for SAN fabric design.

• Design the structure so that there are no more than three switches between two end devices.
• It is desirable that the factory consist of no more than 31 switches.
• It is worth setting the Domain ID manually before introducing a new switch into the fabric - it improves manageability and helps to avoid problems of the same Domain ID, in cases, for example, of reconnecting a switch from one fabric to another.
• Have multiple equivalent routes between each storage device and the initiator.
• In cases of uncertain performance requirements, assume a ratio of the number of Nx ports (for end devices) to the number of ISL ports as 6:1 (EMC recommendation) or 7:1 (Brocade recommendation). This ratio called oversubscription.
• Zoning recommendations:
  - use informative names of zones and zone-sets;
  - use WWPN zoning, not Port-based (based on device addresses, not physical ports of a specific switch);
  - each zone - one initiator;
  - clean the factory from “dead” zones.
• Have a reserve of free ports and cables.
• Have a reserve of equipment (switches). At the site level - necessarily, perhaps at the factory level.

In the simplest case, a SAN consists of storage systems, switches and servers connected by optical communication channels. In addition to direct disk storage systems, you can connect disk libraries, tape libraries (streamers), devices for storing data on optical disks (CD/DVD and others), etc. to the SAN.

An example of a highly reliable infrastructure in which servers are connected simultaneously to a local network (left) and a storage network (right). This scheme provides access to data located on the storage system in the event of failure of any processor module, switch or access path.

Using SAN allows you to provide:

• centralized resource management of servers and data storage systems;
• connecting new disk arrays and servers without stopping the entire storage system;
• using previously purchased equipment in conjunction with new data storage devices;
• prompt and reliable access to data storage devices located at great distances from servers, *without significant performance losses;
• speeding up the process of data backup and recovery - BURA.

Story

The development of network technologies has led to the emergence of two network solutions for storage systems - Storage Area Network (SAN) for exchanging data at the block level supported by client file systems, and servers for storing data at the Network Attached Storage (NAS) file level. To distinguish traditional storage systems from network ones, another retronym was proposed - Direct Attached Storage (DAS).

The successive DAS, SAN, and NAS that have appeared on the market reflect the evolving chain of communications between the applications that use data and the bytes on the media containing that data. Once upon a time, application programs themselves read and wrote blocks, then drivers appeared as part of the operating system. In modern DAS, SAN and NAS, the chain consists of three links: the first link is the creation of RAID arrays, the second is the processing of metadata that allows binary data to be interpreted in the form of files and records, and the third is services for providing data to the application. They differ in where and how these links are implemented. In the case of DAS, the storage system is “bare”; it only provides the ability to store and access data, and everything else is done on the server side, starting with interfaces and drivers. With the advent of SAN, RAID provision is transferred to the storage system side; everything else remains the same as in the case of DAS. But NAS differs in that metadata is also transferred to the storage system to ensure file access; here the client can only support data services.

The emergence of SAN became possible after the Fiber Channel (FC) protocol was developed in 1988 and approved by ANSI as a standard in 1994. The term Storage Area Network dates back to 1999. Over time, FC gave way to Ethernet, and IP-SAN networks with iSCSI connections became widespread.

The idea of ​​a network-attached storage server (NAS) belongs to Brian Randall of Newcastle University and was implemented in machines running a UNIX server in 1983. This idea was so successful that it was picked up by many companies, including Novell, IBM, and Sun, but ultimately replaced the leaders by NetApp and EMC.

In 1995, Garth Gibson developed the principles of NAS and created object storage systems (OBS). He began by dividing all disk operations into two groups, one that included those that were performed more frequently, such as reading and writing, and the other that were performed less frequently, such as operations with names. He then proposed another container in addition to blocks and files, which he called an object.

OBS features a new type of interface, it is called object-based. Client data services interact with metadata using the Object API. OBS not only stores data, but also supports RAID, stores metadata related to objects, and supports the object interface. DAS and SAN and NAS and OBS coexist over time, but each access type is more suited to a specific type of data and application.

SAN architecture

Network topology

SAN is a high-speed data network designed to connect servers to storage devices. A variety of SAN topologies (point-to-point, Arbitrated Loop, and switching) replace traditional server-to-storage bus connections and provide greater flexibility, performance, and reliability over them. The SAN concept is based on the ability to connect any of the servers to any data storage device running using the Fiber Channel protocol. The principle of interaction of nodes in a SAN with point-to-point topologies or switching is shown in the figures. In an Arbitrated Loop SAN, data transfer occurs sequentially from node to node. In order to begin data transmission, the transmitting device initiates arbitration for the right to use the data transmission medium (hence the name of the topology - Arbitrated Loop).

The transport basis of SAN is the Fiber Channel protocol, which uses both copper and fiber-optic device connections.

SAN components

SAN components are classified as follows:

• Data storage resources;
• Devices implementing SAN infrastructure;

Host Bus Adapters

Storage Resources

Storage resources include disk arrays, tape drives, and Fiber Channel libraries. Storage resources realize many of their capabilities only when included in the SAN. So disk arrays upper class can replicate data between arrays over Fiber Channel networks, and tape libraries can transfer data to tape directly from disk arrays with a Fiber Channel interface, bypassing the network and servers (Serverless backup). The most popular in the market are disk arrays from EMC, Hitachi, IBM, Compaq (Storage Works family, which Compaq inherited from Digital), and among tape library manufacturers, StorageTek, Quantum/ATL, and IBM should be mentioned.

Devices implementing SAN infrastructure

Devices that implement the SAN infrastructure are Fiber Channel switches (FC switches), hubs (Fiber Channel Hub) and routers (Fiber Channel-SCSI routers). Hubs are used to combine devices operating in Fiber Channel Arbitrated Loop (FC_AL) mode ). The use of hubs allows you to connect and disconnect devices in a loop without stopping the system, since the hub automatically closes the loop if a device is disconnected and automatically opens the loop if a new device is connected to it. Each loop change is accompanied by a complex process of its initialization. The initialization process is multi-stage, and until it is completed, data exchange in the loop is impossible.

All modern SANs are built on switches that allow for a full-fledged network connection. Switches can not only connect Fiber Channel devices, but also limit access between devices, for which so-called zones are created on switches. Devices placed in different zones, cannot exchange information with each other. The number of ports in a SAN can be increased by connecting switches to each other. A group of interconnected switches is called a Fiber Channel Fabric or simply Fabric. The connections between switches are called Interswitch Links, or ISL for short.

Software

The software allows you to implement redundancy of server access paths to disk arrays and dynamic load distribution between paths. For most disk arrays, there is a simple way to determine that ports accessible through different controllers belong to the same disk. Specialized software maintains a table of access paths to devices and ensures that paths are disconnected in the event of a disaster, dynamically connecting new paths and distributing the load between them. As a rule, disk array manufacturers offer specialized software of this type for their arrays. VERITAS Software produces VERITAS Volume Manager software, designed to organize logical disk volumes from physical disks and provide redundancy of disk access paths, as well as load distribution between them for most known disk arrays.

Protocols used

Low-level protocols are used in storage networks:

• Fiber Channel Protocol (FCP), SCSI transport over Fiber Channel. The most commonly used protocol at the moment. Available in 1 Gbit/s, 2 Gbit/s, 4 Gbit/s, 8 Gbit/s and 10 Gbit/s options.
• iSCSI, SCSI transport over TCP/IP.
• FCoE, FCP/SCSI transport over pure Ethernet.
• FCIP and iFCP, encapsulation and transmission of FCP/SCSI in IP packets.
• HyperSCSI, SCSI transport over Ethernet.
• FICON transport over Fiber Channel (used only by mainframes).
• ATA over Ethernet, ATA transport over Ethernet.
• SCSI and/or TCP/IP transport over InfiniBand (IB).

Advantages

• High reliability of access to data located on external storage systems. Independence of the SAN topology from the storage systems and servers used.
• Centralized data storage (reliability, security).
• Convenient centralized switching and data management.
• Transferring intensive I/O traffic to a separate network - offloading the LAN.
• High performance and low latency.
• Scalability and flexibility of the SAN logical fabric
• The geographic size of a SAN, unlike classic DAS, is practically unlimited.
• The ability to quickly distribute resources between servers.
• The ability to build fault-tolerant cluster solutions without additional costs based on an existing SAN.
• A simple backup scheme - all data is in one place.
• Availability additional features and services (snapshots, remote replication).
• High degree of SAN security.

Sharing storage systems typically simplifies administration and adds a fair amount of flexibility, since cables and disk arrays do not need to be physically transported and reconnected from one server to another.

Another advantage is the ability to boot servers directly from the storage network. With this configuration, you can quickly and easily replace a faulty

Information is the driving force modern business and in present moment considered the most valuable strategic asset of any enterprise. The volume of information is growing exponentially along with the growth of global networks and the development of e-commerce. Success in information warfare requires an effective strategy for storing, protecting, sharing, and managing your most important digital asset—data—both today and in the near future.

Managing storage resources has become one of the most pressing strategic issues facing IT departments. Due to the development of the Internet and fundamental changes in business processes, information is accumulating at an unprecedented speed. In addition to the pressing problem of ensuring the possibility of constantly increasing the volume of stored information, the problem of ensuring the reliability of data storage and constant access to information is no less urgent on the agenda. For many companies, the “24 hours a day, 7 days a week, 365 days a year” data access formula has become the norm.

In the case of a separate PC, a data storage system (DSS) can be understood as a separate internal hard drive or disk system. When it comes to corporate storage systems, we can traditionally distinguish three technologies for organizing data storage: Direct Attached Storage (DAS), Network Attach Storage (NAS) and Storage Area Network (SAN).

Direct Attached Storage (DAS)

DAS technology involves direct (direct) connection of drives to a server or PC. In this case, storage devices (hard drives, tape drives) can be either internal or external. The simplest case of a DAS system is a single disk inside a server or PC. In addition, a DAS system can also include organizing an internal RAID array of disks using a RAID controller.

It is worth noting that, despite the formal possibility of using the term DAS system in relation to a single disk or an internal array of disks, a DAS system is usually understood as an external rack or basket with disks, which can be considered as an autonomous storage system (Fig. 1). In addition to independent power supply, such standalone DAS systems have a specialized controller (processor) to manage the storage array. For example, such a controller can be a RAID controller with the ability to organize RAID arrays of various levels.

Rice. 1. Example of a DAS storage system

It should be noted that standalone DAS systems can have several external I/O channels, which makes it possible to connect several computers to the DAS system simultaneously.

SCSI (Small Computer Systems Interface), SATA, PATA and Fiber Channel interfaces can be used as interfaces for connecting drives (internal or external) in DAS technology. If SCSI, SATA and PATA interfaces are used primarily for connecting internal drives, then the Fiber Channel interface is used exclusively for connecting external drives and stand-alone storage systems. The advantage of the Fiber Channel interface in this case is that it does not have a strict length limitation and can be used when the server or PC connected to the DAS system is located at a considerable distance from it. SCSI and SATA interfaces can also be used to connect external storage systems (in this case, the SATA interface is called eSATA), however, these interfaces have a strict limitation on the maximum length of the cable connecting the DAS system and the connected server.

The main advantages of DAS systems include their low cost (compared to other storage solutions), ease of deployment and administration, as well as high speed of data exchange between the storage system and the server. Actually, it is precisely because of this that they have gained great popularity in the segment of small offices and small corporate networks. At the same time, DAS systems also have their drawbacks, which include poor controllability and suboptimal utilization of resources, since each DAS system requires the connection of a dedicated server.

Currently, DAS systems occupy a leading position, but the share of sales of these systems is constantly decreasing. DAS systems are gradually being replaced by either universal solutions with the possibility of smooth migration from NAS systems, or systems that provide the possibility of using them both as DAS and NAS and even SAN systems.

DAS systems should be used when it is necessary to increase the disk space of one server and move it outside the chassis. DAS systems can also be recommended for use for workstations that process large volumes of information (for example, for non-linear video editing stations).

Network Attached Storage (NAS)

NAS systems are network systems data storage directly connected to the network in the same way as a network print server, router or any other network device (Fig. 2). In fact, NAS systems represent an evolution of file servers: the difference between a traditional file server and a NAS device is about the same as between a hardware network router and a software router based on a dedicated server.

Rice. 2. Example of a NAS storage system

To understand the difference between a traditional file server and a NAS device, let's remember that a traditional file server is a dedicated computer (server) that stores information available to network users. To store information, hard drives installed in the server can be used (as a rule, they are installed in special baskets), or DAS devices can be connected to the server. The file server is administered using the server operating system. This approach to organizing data storage systems is currently the most popular in the segment of small local networks, but it has one significant drawback. The fact is that a universal server (and even in combination with a server operating system) is by no means a cheap solution. At the same time, most of the functionality inherent in a universal server is simply not used in a file server. The idea is to create an optimized file server with an optimized operating system and a balanced configuration. This is exactly the concept that a NAS device embodies. In this sense, NAS devices can be considered “thin” file servers, or, as they are otherwise called, filers.

In addition to an optimized OS, freed from all functions not related to file system maintenance and data input/output implementation, NAS systems have a file system optimized for access speed. NAS systems are designed in such a way that all their computing power is focused exclusively on file serving and storage operations. The operating system itself is located in flash memory and is preinstalled by the manufacturer. Naturally, with the release of a new version of the OS, the user can independently “reflash” the system. Connecting NAS devices to the network and configuring them is a fairly simple task and can be done by any experienced user, not to mention a system administrator.

Thus, compared to traditional file servers, NAS devices are more powerful and less expensive. Currently, almost all NAS devices are designed for use in Ethernet networks (Fast Ethernet, Gigabit Ethernet) based on TCP/IP protocols. NAS devices are accessed using special file access protocols. The most common file access protocols are CIFS, NFS and DAFS.

CIFS(Common Internet File System System) is a protocol that provides access to files and services on remote computers(including the Internet) and uses a client-server interaction model. The client creates a request to the server to access files, the server fulfills the client's request and returns the result of its work. The CIFS protocol is traditionally used on local networks running Windows OS to access files. CIFS uses the TCP/IP protocol to transport data. CIFS provides functionality similar to FTP (File Transfer Protocol) but gives clients improved control over files. It also allows you to share file access between clients using blocking and automatic recovery connection with the server in case of network failure.

Protocol NFS(Network File System) is traditionally used on UNIX platforms and is a combination of a distributed file system and a network protocol. The NFS protocol also uses a client-server communication model. The NFS protocol allows files on a remote host (server) to be accessed as if they were on the user's computer. NFS uses the TCP/IP protocol to transport data. To operate NFS on the Internet, the WebNFS protocol was developed.

Protocol DAFS(Direct Access File System) is a standard file access protocol that is based on NFS. This protocol allows application tasks to transfer data bypassing the operating system and its buffer space directly to transport resources. The DAFS protocol provides high file I/O speeds and reduces processor load by significantly reducing the number of operations and interrupts typically required when processing network protocols.

DAFS was designed for use in cluster and server environments for databases and a variety of Internet applications focused on continuous operation. It provides the lowest latency for accessing file shares and data, and also supports intelligent system and data recovery mechanisms, which makes it attractive for use in NAS systems.

Summarizing the above, NAS systems can be recommended for use in multi-platform networks in cases where network access to files is required and ease of installation of data storage system administration is quite important factors. An excellent example is the use of a NAS as a file server in the office of a small company.

Storage Area Network (SAN)

Actually, SAN is no longer a separate device, but a comprehensive solution, which is a specialized network infrastructure for data storage. Storage networks are integrated as separate specialized subnets into a local (LAN) or wide area (WAN) network.

Essentially, SANs connect one or more servers (SAN servers) to one or more storage devices. SAN networks allow any SAN server to access any storage device without burdening other servers or the local network. In addition, it is possible to exchange data between storage devices without the participation of servers. In fact, SANs allow a very large number of users to store and share information in one place (with fast, centralized access). RAID arrays, various libraries (tape, magneto-optical, etc.), as well as JBOD systems (disk arrays not combined into RAID) can be used as data storage devices.

Data storage networks began to develop intensively and be implemented only in 1999.

Just as local networks can, in principle, be built on the basis of various technologies and standards, various technologies can also be used to build SAN networks. But just as the Ethernet standard (Fast Ethernet, Gigabit Ethernet) has become the de facto standard for local area networks, the Fiber Channel (FC) standard dominates storage area networks. Actually, it was the development of the Fiber Channel standard that led to the development of the SAN concept itself. At the same time, it should be noted that the iSCSI standard is becoming increasingly popular, on the basis of which it is also possible to build SAN networks.

Along with speed parameters, one of the most important advantages of Fiber Channel is the ability to operate over long distances and topology flexibility. The concept of building a storage network topology is based on the same principles as traditional local area networks based on switches and routers, which greatly simplifies the construction of multi-node system configurations.

It is worth noting that the Fiber Channel standard uses both fiber optic and copper cables to transmit data. When organizing access to geographically remote nodes at a distance of up to 10 km, standard equipment and single-mode optical fiber are used for signal transmission. If the nodes are separated over a greater distance (tens or even hundreds of kilometers), special amplifiers are used.

SAN network topology

A typical SAN network based on the Fiber Channel standard is shown in Fig. 3. The infrastructure of such a SAN network consists of storage devices with a Fiber Channel interface, SAN servers (servers connected both to the local network via an Ethernet interface and to the SAN network via a Fiber Channel interface) and a switching fabric (Fiber Channel Fabric) , which is built on the basis of Fiber Channel switches (hubs) and is optimized for transmitting large blocks of data. Network users access the data storage system through SAN servers. It is important that the traffic inside the SAN network is separated from the IP traffic of the local network, which, of course, reduces the load on the local network.

Rice. 3. Typical SAN network diagram

Advantages of SAN networks

The main advantages of SAN technology include high performance, high level of data availability, excellent scalability and manageability, the ability to consolidate and virtualize data.

Fiber Channel switch fabrics with a non-blocking architecture allow multiple SAN servers to simultaneously access storage devices.

With a SAN architecture, data can easily move from one storage device to another, allowing for optimized data placement. This is especially important when multiple SAN servers require simultaneous access to the same storage devices. Note that the process of data consolidation is not possible when using other technologies, such as, for example, when using DAS devices, that is, data storage devices directly connected to servers.

Another opportunity provided by SAN architecture is data virtualization. The idea of ​​virtualization is to provide SAN servers with access not to individual storage devices, but to resources. That is, servers should “see” not storage devices, but virtual resources. For the practical implementation of virtualization, a special virtualization device can be placed between SAN servers and disk devices, to which storage devices are connected on one side, and SAN servers on the other. In addition, many modern FC switches and HBAs provide the ability to implement virtualization.

The next opportunity provided by SAN networks is the implementation of remote data mirroring. The principle of data mirroring is to duplicate information on several media, which increases the reliability of information storage. An example of the simplest case of data mirroring is combining two disks into a RAID level 1 array. In this case, the same information is written simultaneously to two disks. The disadvantage of this method is the local location of both disks (as a rule, the disks are located in the same basket or rack). Storage networks allow you to overcome this drawback and provide the opportunity to organize mirroring not just of individual data storage devices, but of the SAN networks themselves, which can be hundreds of kilometers away from each other.

Another advantage of SAN networks is the ease of organizing data backup. Traditional backup technology, which is used in most local networks, requires a dedicated Backup server and, most importantly, dedicated network bandwidth. In fact, during the backup operation, the server itself becomes unavailable to local network users. In fact, this is why backups are usually performed at night.

The architecture of storage networks allows a fundamentally different approach to the problem of backup. In this case, the Backup server is integral part SAN network and connects directly to the switch fabric. In this case, Backup traffic is isolated from local network traffic.

Equipment used to create SAN networks

As already noted, deploying a SAN network requires storage devices, SAN servers, and equipment to build a switch fabric. Switch fabrics include both devices physical level(cables, connectors), and connection devices (Interconnect Device) for connecting SAN nodes with each other, Translation devices that perform the functions of converting the Fiber Channel (FC) protocol to other protocols, for example SCSI, FCP, FICON, Ethernet , ATM or SONET.

Cables

As already noted, the Fiber Channel standard allows the use of both fiber optic and copper cables to connect SAN devices. At the same time, different types of cables can be used in one SAN network. Copper cable is used for short distances (up to 30 m), and fiber optic cable is used for both short and distances up to 10 km or more. Both multimode and singlemode fiber optic cables are used, with multimode used for distances up to 2 km, and singlemode for longer distances.

Coexistence various types cables within the same SAN network are provided using special interface converters GBIC (Gigabit Interface Converter) and MIA (Media Interface Adapter).

The Fiber Channel standard has several possible transmission rates (see table). Note that currently the most common FC devices are standards 1, 2 and 4 GFC. This ensures backward compatibility of faster devices with slower ones, that is, a 4 GFC device automatically supports connecting devices of 1 and 2 GFC standards.

Interconnect Device

The Fiber Channel standard allows the use of various network topologies for connecting devices, such as point-to-point, Arbitrated Loop (FC-AL), and switched fabric.

A point-to-point topology can be used to connect a server to a dedicated storage system. In this case, the data is not shared with the SAN servers. In fact, this topology is a variant of a DAS system.

To implement a point-to-point topology, at a minimum, you need a server equipped with a Fiber Channel adapter and a storage device with a Fiber Channel interface.

A split-access ring topology (FC-AL) is a device connection scheme in which data is transferred in a logically closed loop. In an FC-AL ring topology, the connection devices can be hubs or Fiber Channel switches. With hubs, the bandwidth is shared among all nodes in the ring, while each switch port provides protocol bandwidth to each node.

In Fig. Figure 4 shows an example of a split Fiber Channel ring.

Rice. 4. Example of a Fiber Channel ring with shared access

The configuration is similar to the physical star and logical ring used in local area networks based on Token Ring technology. Also, like Token Ring networks, data travels around the ring in one direction, but unlike Token Ring networks, a device can request permission to transmit data rather than wait for an empty token from the switch. Fiber Channel rings with shared access can address up to 127 ports, however, as practice shows, typical FC-AL rings contain up to 12 nodes, and after connecting 50 nodes, performance deteriorates catastrophically.

The topology of the switched communication architecture (Fiber Channel switched-fabric) is implemented on the basis of Fiber Channel switches. In this topology, each device has a logical connection to every other device. In fact, Fiber Channel fabric switches perform the same functions as traditional Ethernet switches. Recall that, unlike a hub, a switch is a high-speed device that provides “everyone-to-everyone” connectivity and handles multiple simultaneous connections. Any node connected to a Fiber Channel switch receives protocol bandwidth.

In most cases, when creating large SAN networks, a mixed topology is used. At the lower level, FC-AL rings are used, connected to low-performance switches, which, in turn, are connected to high-speed switches, providing the highest possible throughput. Multiple switches can be connected to each other.

Broadcast devices

Translation devices are intermediate devices that convert the Fiber Channel protocol to more advanced protocols. high levels. These devices are designed to connect a Fiber Channel network to an external WAN network, a local network, as well as to connect various devices and servers to a Fiber Channel network. Such devices include bridges, Fiber Channel adapters (Host Bus Adapters (HBA), routers, gateways and network adapters. The classification of broadcast devices is shown in Fig. 5.

Rice. 5. Classification of broadcast devices

The most common translation devices are HBA adapters with PCI interface, which are used to connect servers to a Fiber Channel network. Network adapters allow you to connect local Ethernet networks to Fiber Channel networks. Bridges are used to connect storage devices with a SCSI interface to a Fiber Channel-based network. It should be noted that in lately Almost all storage devices that are designed for use in a SAN have built-in Fiber Channel and do not require the use of bridges.

Storage devices

Both hard drives and tape drives can be used as data storage devices in SAN networks. If we talk about possible application configurations hard drives as data storage devices in SAN networks, these can be either JBOD arrays or RAID disk arrays. Traditionally, storage devices for SAN networks are produced in the form of external racks or baskets equipped with a specialized RAID controller. Unlike NAS or DAS devices, devices for SAN systems are equipped with a Fiber Channel interface. At the same time, the disks themselves can have both a SCSI and SATA interface.

In addition to hard drive-based storage devices, tape drives and libraries are widely used in SAN networks.

SAN servers

SAN servers differ from conventional application servers in only one detail. In addition to the Ethernet network adapter, for the server to interact with the local network, they are equipped with an HBA adapter, which allows them to be connected to SAN networks based on Fiber Channel.

Intel Storage Systems

Next we will look at several specific examples Intel storage devices. Strictly speaking, Intel does not produce complete solutions and is engaged in the development and production of platforms and individual components for building data storage systems. Based on these platforms, many companies (including a number of Russian companies) produce complete solutions and sell them under their logos.

Intel Entry Storage System SS4000-E

The Intel Entry Storage System SS4000-E is a NAS device designed for use in small and medium-sized offices and multi-platform local area networks. When using Intel systems Entry Storage System SS4000-E provides shared network access to data for clients based on Windows, Linux and Macintosh platforms. In addition, the Intel Entry Storage System SS4000-E can act as both a DHCP server and a DHCP client.

The Intel Entry Storage System SS4000-E is a compact external rack with the ability to install up to four SATA drives (Fig. 6). Thus, the maximum system capacity can be 2 TB using 500 GB drives.

Rice. 6. Intel Entry Storage System SS4000-E

The Intel Entry Storage System SS4000-E uses a SATA RAID controller that supports RAID levels 1, 5, and 10. Because this system is a NAS device, that is, in fact, a “thin” file server, the data storage system must have a specialized processor, memory and a firmware operating system. The Intel Entry Storage System SS4000-E uses an Intel 80219 processor with a clock frequency of 400 MHz. In addition, the system is equipped with 256 MB DDR memory and 32 MB of flash memory for storing the operating system. The operating system is Linux Kernel 2.6.

To connect to a local network, the system provides a two-channel gigabit network controller. In addition, there are also two USB ports.

The Intel Entry Storage System SS4000-E data storage device supports CIFS/SMB, NFS and FTP protocols, and the device is configured using a web interface.

In the case of using Windows clients (Windows 2000/2003/XP are supported), it is additionally possible to implement data backup and recovery.

Intel Storage System SSR212CC

The Intel Storage System SSR212CC is a universal platform for creating DAS, NAS and SAN storage systems. This system is housed in a 2 U high housing and is designed for mounting in a standard 19-inch rack (Fig. 7). The Intel Storage System SSR212CC supports installation of up to 12 drives with SATA or SATA II interface (hot-swappable) which allows you to expand the system capacity up to 6 TB using 550 GB drives.

Rice. 7. Intel Storage System SSR212CC

In fact, the Intel Storage System SSR212CC is a full-fledged high-performance server running Red Hat Enterprise Linux 4.0 operating systems, Microsoft Windows Storage Server 2003, Microsoft Windows Server 2003 Enterprise Edition and Microsoft Windows Server 2003 Standard Edition.

The basis of the server is Intel processor Xeon with a clock frequency of 2.8 GHz (FSB frequency 800 MHz, L2 cache size 1 MB). The system supports the use of SDRAM DDR2-400 memory with ECC with a maximum capacity of up to 12 GB (six DIMM slots are provided for installing memory modules).

The Intel Storage System SSR212CC is equipped with two Intel RAID Controller SRCS28Xs with the ability to create RAID arrays of levels 0, 1, 10, 5 and 50. In addition, the Intel Storage System SSR212CC has a dual-channel gigabit network controller.

Intel Storage System SSR212MA

The Intel Storage System SSR212MA is a platform for creating data storage systems in IP SAN networks based on iSCSI.

This system is housed in a 2 U high housing and is designed for mounting in a standard 19-inch rack. The Intel Storage System SSR212MA supports installation of up to 12 SATA drives (hot-swappable), allowing system capacity to be expanded up to 6 TB using 550 GB drives.

In terms of its hardware configuration, the Intel Storage System SSR212MA is no different from the Intel Storage System SSR212CC.

In this article, we will look at what types of data storage systems (SDS) exist today, and we will also consider one of the main components of SDS - external connection interfaces (interaction protocols) and drives on which data is stored. We will also make a general comparison of them based on the capabilities provided. For examples, we will refer to the storage system line provided by DELL.

• Examples of DAS models
• Examples of NAS models
• Examples of SAN models
• Types of storage media and protocol for interaction with storage systems Fiber Channel Protocol
• iSCSI protocol
• SAS protocol
• Comparison of storage system connection protocols

Existing types of storage systems

In the case of a separate PC, the storage system can be understood as an internal hard drive or disk system (RAID array). When it comes to data storage systems at different levels of enterprises, then traditionally three technologies for organizing data storage can be distinguished:

• Direct Attached Storage (DAS);
• Network Attach Storage (NAS);
• Storage Area Network (SAN).

DAS (Direct Attached Storage) devices are a solution when a data storage device is connected directly to a server or workstation, usually via an interface using the SAS protocol.

NAS (Network Attached Storage) devices are a free-standing integrated disk system, essentially a NAS server, with its own specialized OS and a set of useful functions for quickly starting the system and providing access to files. The system connects to a regular computer network (LAN), and is a quick solution to the problem of lack of free disk space available to users of this network.

A Storage Area Network (SAN) is a special dedicated network that connects storage devices with application servers, usually based on the Fiber Channel protocol or the iSCSI protocol.

Now let's take a closer look at each of the above types of storage systems, their positive and negative sides.

DAS (Direct Attached Storage) storage system architecture

The main advantages of DAS systems include their low cost (compared to other storage solutions), ease of deployment and administration, as well as high speed of data exchange between the storage system and the server. In fact, it is precisely because of this that they have gained great popularity in the segment of small offices, hosting providers and small corporate networks. At the same time, DAS systems also have their drawbacks, which include non-optimal utilization of resources, since each DAS system requires the connection of a dedicated server and allows you to connect a maximum of 2 servers to a disk shelf in a certain configuration.

Figure 1: Direct Attached Storage Architecture

• Fairly low cost. Essentially, this storage system is a disk basket with hard drives located outside the server.
• Easy to deploy and administer.
• High speed of exchange between the disk array and the server.

• Low reliability. If the server to which this storage is connected fails, the data will no longer be available.
• Low degree of resource consolidation - all capacity is available to one or two servers, which reduces the flexibility of data distribution between servers. As a result, it is necessary to purchase either more internal hard drives or install additional disk shelves for other server systems
• Low resource utilization.

Examples of DAS models

From interesting models For devices of this type, I would like to note the DELL PowerVault MD series lineup. The initial models of disk shelves (JBOD) MD1000 and MD1120 allow you to create disk arrays with up to 144 disks. This is achieved due to the modularity of the architecture; up to 6 devices can be connected to the array, three disk shelves per RAID controller channel. For example, if we use a rack of 6 DELL PowerVault MD1120, then we will implement an array with an effective data volume of 43.2 TB. Such disk enclosures are connected by one or two SAS cables to external ports of RAID controllers installed in Dell PowerEdge servers and are managed by the management console of the server itself.

If there is a need to create an architecture with high fault tolerance, for example, to create a failover cluster of MS Exchange or a SQL server, then the DELL PowerVault MD3000 model is suitable for these purposes. This system already has active logic inside the disk enclosure and is completely redundant due to the use of two built-in active-active RAID controllers that have a mirrored copy of the data buffered in cache memory.

Both controllers process data read and write streams in parallel, and if one of them fails, the second “pick up” data from the neighboring controller. At the same time, connection to a low-level SAS controller inside 2 servers (cluster) can be made via several interfaces (MPIO), which provides redundancy and load balancing in Microsoft environments. To expand disk space, you can connect 2 additional MD1000 disk shelves to the PowerVault MD3000.

NAS (Network Attached Storage) storage system architecture

NAS technology (networked storage subsystems, Network Attached Storage) is developing as an alternative to universal servers that carry many functions (printing, applications, fax server, e-mail etc.). In contrast, NAS devices perform only one function - file server. And they try to do it as best, easier and faster as possible.

NAS connect to a LAN and provide data access to an unlimited number of heterogeneous clients (clients with different OSes) or other servers. Currently, almost all NAS devices are designed for use in Ethernet networks (Fast Ethernet, Gigabit Ethernet) based on TCP/IP protocols. NAS devices are accessed using special file access protocols. The most common file access protocols are CIFS, NFS and DAFS. Such servers contain specialized operating systems, such as MS Windows Storage Server.

Figure 2: Network Attached Storage Architecture

• The cheapness and availability of its resources not only for individual servers, but also for any computers in the organization.
• Ease of sharing resources.
• Ease of deployment and administration
• Versatility for clients (one server can serve MS, Novell, Mac, Unix clients)

• Accessing information through “network file system” protocols is often slower than accessing a local disk.
• Most inexpensive NAS servers do not provide the fast and flexible method of accessing data at the block level inherent in SAN systems, rather than at the file level.

Examples of NAS models

At the moment, classic NAS solutions such as PowerVault NF100/500/600. These are systems based on mainstream 1 and 2 processor Dell servers, optimized for the rapid deployment of NAS services. They allow you to create file storage up to 10 TB (PowerVault NF600) using SATA or SAS drives and connecting this server to a LAN. There are also higher-performance integrated solutions, such as PowerVault NX1950, which can accommodate 15 drives and can be expanded to 45 by connecting additional MD1000 disk enclosures.

A major advantage of the NX1950 is the ability to work not only with files, but also with data blocks at the iSCSI protocol level. Also, the NX1950 variety can work as a gateway, allowing file access to iSCSI-based storage systems (with block access method), for example MD3000i or Dell EqualLogic PS5x00.

SAN (Storage Area Network) storage system architecture

A Storage Area Network (SAN) is a special dedicated network that connects storage devices with application servers, usually based on the Fiber Channel protocol, or on the increasingly popular iSCSI protocol. Unlike NAS, SAN has no concept of files: file operations are performed on servers connected to the SAN. SAN operates in blocks, like a large hard drive. The ideal result of a SAN is the ability of any server running any operating system to access any part of the disk capacity located in the SAN. SAN end elements are application servers and storage systems (disk arrays, tape libraries, etc.). And between them, as in a regular network, there are adapters, switches, bridges, and hubs. ISCSI is a more "friendly" protocol because it is based on the standard Ethernet infrastructure - network cards, switches, cables. Moreover, iSCSI-based storage systems are the most popular for virtualized servers due to the ease of setting up the protocol.

Figure 3: Storage Area Network Architecture

• High reliability of access to data located on external storage systems. Independence of the SAN topology from the storage systems and servers used.
• Centralized data storage (reliability, security).
• Convenient centralized switching and data management.
• Moves heavy I/O traffic to a separate network, offloading the LAN.
• High performance and low latency.
• Scalability and flexibility of the SAN logical fabric
• The ability to organize backup, remote storage systems and a remote backup and data recovery system.
• The ability to build fault-tolerant cluster solutions without additional costs based on an existing SAN.

• Higher cost
• Difficulty in setting up FC systems
• The need for certification of specialists in FC networks (iSCSI is a simpler protocol)
• More stringent requirements for compatibility and component validation.
• Due to the high cost, the appearance of DAS “islands” in networks based on the FC protocol, when single servers with internal disk space, NAS servers or DAS systems due to budget constraints.

Examples of SAN models

At the moment, there is a fairly large selection of disk arrays for building SANs, ranging from models for small and medium-sized enterprises, such as the DELL AX series, which allow you to create storage capacities of up to 60 TB, and ending with disk arrays for large corporations, the DELL/EMC CX4 series, they allow you to create storage capacities of up to 950 TB. There is an inexpensive solution based on iSCSI, this is the PowerVault MD3000i - the solution allows you to connect up to 16-32 servers, you can install up to 15 disks in one device, and expand the system with two MD1000 shelves, creating a 45TB array.

The Dell EqualLogic system based on the iSCSI protocol deserves special mention. It is positioned as an enterprise-scale storage system and is comparable in price to Dell systems | EMC CX4, with a modular port architecture that supports both the FC protocol and the iSCSI protocol. The EqualLogic system is peer-to-peer, meaning each disk enclosure has active RAID controllers. When these arrays are connected into a single system, the performance of the disk pool increases smoothly with the increase in the available data storage volume. The system allows you to create arrays of more than 500TB, can be configured in less than an hour, and does not require specialized knowledge of administrators.

The licensing model is also different from the rest and already includes in the initial price all possible snapshot options, replication and integration tools into various OSes and applications. This system is considered one of the most fast systems in tests for MS Exchange (ESRP).

Types of storage media and protocol for interaction with storage systems

Having decided on the type of storage system that is most suitable for you to solve certain problems, you need to move on to choosing a protocol for interacting with the storage system and selecting drives that will be used in the storage system.

Currently, SATA and SAS drives are used to store data in disk arrays. Which disks to choose for storage depends on specific tasks. Several facts are worth noting.

SATA II drives:

• Single disk sizes up to 1 TB available
• Rotation speed 5400-7200 RPM
• I/O speed up to 2.4 Gbps
• The time between failures is approximately two times less than that of SAS drives.
• Less reliable than SAS drives.
• About 1.5 times cheaper than SAS disks.

• Single disk sizes up to 450 GB available
• Rotation speed 7200 (NearLine), 10000 and 15000 RPM
• I/O speed up to 3.0 Gbps
• MTBF is twice as long as SATA II drives.
• More reliable drives.

Important! Last year, industrial production of SAS disks with a reduced rotation speed of 7200 rpm (Near-line SAS Drive) began. This made it possible to increase the amount of data stored on one disk to 1 TB and reduce the energy consumption of disks with a high-speed interface. Despite the fact that the cost of such drives is comparable to the cost of SATA II drives, and the reliability and I/O speed remains at the level of SAS drives.

Thus, at this moment it is worth really thinking seriously about the data storage protocols that you are going to use within the framework of enterprise storage.

Until recently, the main protocols for interaction with storage systems were FibreChannel and SCSI. Now SCSI has been replaced by the iSCSI and SAS protocols, having expanded its functionality. Let's look below at the pros and cons of each of the protocols and the corresponding interfaces for connecting to the storage system.

Fiber Channel Protocol

In practice, modern Fiber Channel (FC) has speeds of 2 Gbit/Sec (Fiber Channel 2 Gb), 4 Gbit/Sec (Fiber Channel 4 Gb) full-duplex or 8 Gbit/Sec, that is, this speed is provided simultaneously in both directions. At such speeds, connection distances are practically unlimited - from the standard 300 meters on the most “ordinary” equipment to several hundred or even thousands of kilometers when using specialized equipment. The main advantage of the FC protocol is the ability to combine many storage devices and hosts (servers) into a single storage area network (SAN). At the same time, there is no problem of distributing devices over long distances, the possibility of channel aggregation, the possibility of redundant access paths, “hot plugging” of equipment, and greater noise immunity. But on the other hand, we have a high cost and high labor intensity for installing and maintaining disk arrays using FC.

Important! The two terms Fiber Channel protocol and Fiber Channel interface should be distinguished. The Fiber Channel protocol can operate on different interfaces - both on a fiber-optic connection with different modulations, and on copper connections.

• Flexible storage scalability;
• Allows you to create storage systems over significant distances (but shorter than in the case of the iSCSI protocol; where, in theory, the entire global IP network can act as a carrier.
• Great reservation possibilities.

• High cost of the solution;
• Even higher costs when organizing an FC network over hundreds or thousands of kilometers
• High labor intensity during implementation and maintenance.

Important! In addition to the emergence of the FC8 Gb/s protocol, the emergence of the FCoE (Fibre Channel over Ethernet) protocol is expected, which will allow the use of standard IP networks to organize the exchange of FC packets.

iSCSI protocol

iSCSI (IP-based SCSI encapsulation) allows users to create IP-based storage networks using Ethernet infrastructure and RJ45 ports. Thus, iSCSI allows you to overcome the limitations of directly attached storage, including the inability to share resources across servers and the inability to expand capacity without shutting down applications. The transfer speed is currently limited to 1 Gb/s (Gigabit Ethernet), but given speed is sufficient for most business applications of medium-sized enterprises and this is confirmed by numerous tests. It is interesting that it is not so much the data transfer speed on one channel that is important, but the algorithms of operation of RAID controllers and the ability to aggregate arrays into a single pool, as is the case with DELL EqualLogic, when three 1GB ports are used on each array, and the load is balanced among the arrays one group.

It is important to note that SANs based on the iSCSI protocol provide the same benefits as SANs using the Fiber Channel protocol, but at the same time, the procedures for deploying and managing the network are simplified, and the cost of this storage system is significantly reduced.

• High availability;
• Scalability;
• Ease of administration, as Ethernet technology is used;
• Lower price for organizing a SAN using the iSCSI protocol than using FC.
• Easy integration into virtualization environments

• There are certain restrictions on use of storage systems with the iSCSI protocol with some OLAP and OLTP applications, with Real Time systems and when working with a large number of video streams in HD format
• High-level storage systems based on iSCSI, as well as storage systems with the FC protocol, require the use of fast, expensive Ethernet switches
• It is recommended to use either dedicated Ethernet switches or VLAN organization to separate data streams. Network design is no less important part of the project than when developing FC networks.

Important! Manufacturers promise to soon mass produce SANs based on the iSCSI protocol with support for data transfer rates of up to 10 Gb/s. Also in preparation final version DCE (Data Center Ethernet) protocol, the massive appearance of devices supporting the DCE protocol is expected by 2011.

From the point of view of the interfaces used, the iSCSI protocol uses 1Gbit/C Ethernet interfaces, and they can be either copper or fiber-optic interfaces when operating over long distances.

SAS protocol

The SAS protocol and interface of the same name are designed to replace parallel SCSI and achieve higher throughput than SCSI. Although SAS uses a serial interface as opposed to the parallel interface used by traditional SCSI, SCSI commands are still used to control SAS devices. SAS allows you to provide a physical connection between a data array and several servers over short distances.

• Reasonable price;
• Ease of storage consolidation - although SAS-based storage cannot connect to as many hosts (servers) as SAN configurations that use the FC or iSCSI protocols, when using the SAS protocol there are no difficulties with additional equipment to organize shared storage for several servers.
• The SAS protocol allows for higher throughput using 4 channel connections within a single interface. Each channel provides 3 Gb/s, which allows you to achieve a data transfer rate of 12 Gb/s (currently the highest data transfer speed for storage systems).

• Limited reach - the cable length cannot exceed 8 meters. Thus, storage with a connection via the SAS protocol will be optimal only when the servers and arrays are located in the same rack or in the same server room;
• The number of connected hosts (servers) is usually limited to several nodes.

Important! In 2009, SAS technology is expected to appear with a data transfer rate over one channel of 6 Gbit/s, which will significantly increase the attractiveness of using this protocol.

Comparison of storage connection protocols

Below is a summary table comparing the capabilities of various protocols for interaction with storage systems.

Thus, the presented solutions, at first glance, are quite clearly divided according to their compliance with customer requirements. However, in practice, everything is not so simple; additional factors are included in the form of budget restrictions, the dynamics of the organization’s development (and the dynamics of increasing the volume of stored information), industry specifics, etc.

SAN switches

SAN switches are used as a central switching device for SAN network nodes. You plug one end of the optical cable into a connector on your server adapter or controller disk array, and the other to a port on the switch. A switch can be compared to a set of wires that are crossed in such a way as to allow each device on the network to “talk” over one wire to every other device on the network at the same time. That is, in other words, all subscribers can talk at the same time.
One or more switches interconnected form a fabric. A single fabric can consist of one or more switches (up to 239 currently). Therefore, a factory can be defined as a network consisting of interconnected switches. A SAN can consist of several fabrics. Most SANs consist of at least two fabrics, one of which is a backup fabric.
You can connect servers and storage to a SAN using a single switch, but it is good practice to use two switches to avoid data loss and downtime if one of them fails. Figure 1 shows a typical fabric that uses two switches to connect servers to a disk array.

Fig 1. The simplest factory using 2 switches.

As the number of servers and storage in your SAN increases, you simply add switches.

Figure 2. SAN Fabric expansion

Modular or regular switches (modular switches)

SAN switches come in a variety of sizes from 8 to hundreds of ports. Most modular switches come with 8 or 16 ports. The latest trend is the ability to increase the number of ports on a purchased switch in increments of 4. A typical example of such a switch is the Qlogic SANbox 5200 (Fig. 3). You can purchase this product with 8 ports in the base, and then expand it to 16 in one module and up to 64 ports (!) in four modules, interconnected by 10 Gigabit FC.

Fig 3. Qlogic SANbox 5200 - four-module stack with 64 ports

Director switches

Directors are much more expensive than modular switches and typically contain hundreds of ports (Figure 4). Directors can be seen at the center of very large switched fabrics as the core of the network. Directors have exceptional fault tolerance and keep the entire infrastructure running 24 hours a day, 7 days a week. They allow you to carry out routine maintenance and replace modules on the fly.

Rice. 4. SilkWorm 1200 128 port and McData InterPid 6140

The director consists of a platform, hot-swap port modules (usually 12 or 16 ports), and hot-swap processor modules (usually dual-processor). The director can be purchased with 32 ports and can be expanded to 128 - 140 ports.
IN corporate networks SANs are typically used by directors as the core of the network. Modular switches are connected to them as terminal (edge) switches. These, in turn, are connected to servers and storage. This topology is called core-to-edge topology and allows you to scale the network to thousands of ports (Fig. 5).

Rice. 5. Core-edge topology using directors.

SAN routers or multiprotocol switches

SAN routers are used to connect remote SAN islands into a single network to solve problems of disaster protection, consolidation of storage resources, organizing procedures for back-up of data from remote departments to tape and disk resources of the main data center, etc. (Figure 6.). Consolidation of remote SAN networks into a single resource is the next step in the evolution of data storage networks after the introduction of SAN in the head office and departments of enterprises (Fig. 7).

Rice. 6: McDATA Eclipse 1620, 3300 and 4300

Rice. 7: Consolidating remote SANs into a single resource

SAN islands can be connected using the FC protocol and conventional modular switches or directors, through a single mode optical cable (single mode cable or dark fiber) or using multiplexing equipment (DWDM). However, this method will not allow you to go beyond the city limits (radius 70 km). For greater distances, you will need the Fiber Channel over IP protocol (FCIP, http://www.iscsistorage.com/ipstorage.htm), implemented in McData's Eclipse routers (Fig. 6). FCIP wraps each FC frame in an IP packet for transport over the IP network. The receiving side unpacks the IP packet and takes out the original FC frame from there for further transmission over the local FC network. Here the distances are not limited. It's all about the speed of your IP channel.

FC Cable Types

Fiber optic or copper cable is used as a physical data transmission medium in FC networks. Copper cable is twisted pair in the shell and was used mainly for local connections in FC 1Gbit/s networks. Modern FC 2Gbit/s networks mainly use fiber optic cable.
There are two types of fiber optic cable: single-mode and multi-mode.

Single mode cable (long wave)

In a single mode (SM) cable, there is only one path for the light wave to travel. The core size is usually 8.3 microns. Single-mode cables are used in applications that require low signal attenuation and high data rates, such as long distances between two systems or network devices. For example, between a server and a storage facility, the distance between which is several tens of kilometers.

The maximum distance between two FC 2Gbit network nodes connected by a single-mode cable is 80 km without repeaters.

Multimode cable (short wave)

Multimode (MM) cable is capable of transmitting multiple wavelengths of light along a single fiber because the relatively large core size allows light to travel at different angles (refraction). Typical core sizes for MM are 50 µm and 62.5 µm. Multimode fiber connections are best suited for devices operating over short distances. Inside an office, building.

The maximum distance over which a multimode cable supports a speed of 2 Gbit/s is 300 (50um) and 150m (62.5um).

Cable connector types

FC cable connectors are:

Transceiver types (GBIC types)

Devices for converting light into an electrical signal and vice versa are called transceivers. They are also called GBIC (Gigabit Interface Connectors). The transceiver is located on the FC adapter board (FC HBA), usually it is soldered into it, in the switch - in the form of a removable module (see figure) and on a storage device in one form or another.

Transceivers are:

SFP-LC	HSSDC2

Removable transceiver modules (SFP)

HSSDC2: for 1/2Gbit FC for copper cable
SFP-LC: (Small Form Factor Pluggable LC) 1/2Gbit FC Short/Long wave for fiber optic cable with LC connector
SFP-SC: (Small Form Factor Pluggable SC) 1/2Gbit FC Short/Long wave for fiber optic cable with SC connector