What is a Storage Area Network (SAN) and how does it work?

A Storage Area Network (SAN) is a spe­cial­ized, high-per­for­mance network that connects servers with shared storage devices, allowing block-based access. It is primarily used in data centers to ef­fi­cient­ly and centrally manage large amounts of data and storage capacity.

What is a Storage Area Network (SAN)?

A Storage Area Network (SAN) is a storage network designed to connect disk systems to server systems. In a SAN, the entire storage capacity—provided by storage media like HDDs, SSDs, disk arrays (disk sub­sys­tems), or tape libraries—is con­sol­i­dat­ed into a virtual storage unit and centrally managed. Access to the SAN storage is achieved through ap­pro­pri­ate­ly con­fig­ured servers. The storage network is operated parallel to a Local Area Network (LAN) and provides the entire mass storage to this computer network. SAN can thus be viewed as a secondary network dedicated solely to data transport to mass storage.

SAN servers act as the con­nec­tion point. These don’t need to be located at the same place as the in­di­vid­ual disk drives. Ad­di­tion­al­ly, the SAN operates in­de­pen­dent­ly of the operating system of the computers accessing the storage. This makes a Storage Area Network ideal for cross-platform data man­age­ment.

SAN systems were developed with the un­der­stand­ing that dedicated disk drives in server systems often lead to man­age­ment issues. With shared virtual storage capacity, Storage Area Networks are sig­nif­i­cant­ly more effective and flexible in handling large volumes of data. Unlike simple network storage solutions like Network Attached Storage (NAS), SAN offers the advantage that the LAN is not burdened by data access to the mass storage due to the ad­di­tion­al network.

System ar­chi­tec­ture of a Storage Area Network

Setting up a Storage Area Network is con­sid­ered complex and expensive, as it requires a complete system ar­chi­tec­ture to be purchased with sometimes very costly hardware. Apart from cabling, three basic com­po­nents are needed: SAN servers, Fibre Channel switches, and storage media.

• Fibre Channel fabric: In IT, a “fabric” refers to a network of in­ter­con­nect­ed cables and switches that ensures high re­dun­dan­cy through multiple cross-links. This ar­chi­tec­ture delivers not only im­pres­sive data through­put but also out­stand­ing bandwidth and re­li­a­bil­i­ty. At the heart of a Storage Area Network (SAN) lies such a fabric, made up of Fibre Channel switches and fiber-optic cables. All devices within the SAN connect to the Fibre Channel switch, which dy­nam­i­cal­ly manages the real-time data paths between senders and receivers. Fibre Channel was developed as a standard interface for storage networks and supports con­sis­tent, high-speed data transfers — with rates of up to 16 Gbit/s.
• Storage elements: In Storage Area Networks, disk arrays are generally used for data storage. These are devices con­tain­ing multiple hard disk drives (HDDs) or solid-state drives (SSDs) for mass storage. To ensure high avail­abil­i­ty of stored data, modern disk arrays have a con­troller re­spon­si­ble for redundant data storage and load balancing during data transfer. This increases data security and enhances transfer rates. The im­ple­men­ta­tion of a redundant storage process usually involves RAID-systems (Redundant Array of In­de­pen­dent Disks), which combine in­di­vid­ual physical disk drives of a disk array into a logical drive. Al­ter­na­tive­ly, tape libraries or in­di­vid­ual disk drives can also be in­te­grat­ed into a SAN.
• SAN servers: To ensure smooth in­ter­ac­tion with the virtual storage unit, each SAN requires specif­i­cal­ly con­fig­ured servers that manage data access, acting as a link between the storage network and the devices connected in the LAN. These SAN servers are connected to the Fibre Channel switch via special hardware in­ter­faces known as Host Bus Adapters (HBA).

How exactly does a Storage Area Network work?

A SAN is based on a network structure specif­i­cal­ly designed for storage access, separate from con­ven­tion­al data networks like a LAN. The foun­da­tion of the Storage Area Network includes Fibre Channel or iSCSI con­nec­tions, through which servers or hosts com­mu­ni­cate with storage resources.

The pre­vi­ous­ly mentioned storage elements provide block-based storage to the SAN. Com­mu­ni­ca­tion is conducted through SAN switches, which operate similarly to tra­di­tion­al network switches but are designed for high data rates and minimal latency.

Through what are known as LUNs (Logical Unit Numbers), storage is allocated to in­di­vid­ual servers. These servers access the LUNs through special Host Bus Adapters (HBA) or iSCSI ini­tia­tors, as if they were locally attached drives. The Storage Area Network ensures that these storage accesses occur in parallel, reliably, and without in­ter­fer­ence. The man­age­ment and al­lo­ca­tion of storage resources are handled by cen­tral­ized man­age­ment software, which controls access rights and avail­abil­i­ty. This central or­ga­ni­za­tion allows storage resources to be flexibly expanded, re­as­signed, or mirrored even while in operation.

How to set up a SAN System step by step

A Storage Area Network is designed for high avail­abil­i­ty. In IT, this refers to the ability of a computer system to ensure the smooth operation of business-critical ap­pli­ca­tions despite the failure of in­di­vid­ual hardware com­po­nents. Setting up a Storage Area Network involves several steps, as shown below.

Step 1: Assessing re­quire­ments and planning

First, it is de­ter­mined what the SAN will be used for. There are various use cases, such as virtual machines, databases, or large data archives. This de­ter­mines how much storage space is needed, how fast access needs to be, and how many servers should be connected. Re­quire­ments for fault tolerance are also con­sid­ered.

Step 2: Selecting and preparing hardware

A SAN, as pre­vi­ous­ly described, consists of several central com­po­nents. To achieve high avail­abil­i­ty, all central com­po­nents are du­pli­cat­ed. This means there are at least two switches, two data paths, dual power supplies, and often two RAID con­trollers. If one part fails, the other au­to­mat­i­cal­ly takes over. This principle is also known as re­dun­dan­cy.

Step 3: Setting up the network

In the next step, the physical con­nec­tion between the devices is es­tab­lished. The servers are connected to the SAN switches via their host bus adapters, as are the storage systems. This con­nec­tion is made via Fibre Channel or iSCSI, using fiber optic cables or special network cables. The goal is to create a separate, fast, and stable network.

Step 4: Con­fig­ur­ing the storage system

On the central storage system, the desired storage structure is then set up. This includes setting up RAID systems to increase fault tolerance. RAID 1 or RAID 10 are common variants where data is always doubly stored on different hard drives. This mirroring is part of the so-called redundant storage cycles and ensures that no data is lost even if a hard drive fails.

In addition, so-called LUNs (Logical Unit Numbers) are defined. Through mul­ti­pathing tech­nolo­gies, servers can si­mul­ta­ne­ous­ly access the same storage resource via multiple paths, further in­creas­ing fault tolerance.

Step 5: In­te­grat­ing the server

The servers that need to access the SAN storage are also prepared ac­cord­ing­ly. They receive the ap­pro­pri­ate drivers for the host bus adapters. Ad­di­tion­al­ly, a mul­ti­pathing software is installed, which au­to­mat­i­cal­ly detects if a path fails and redirects the data traffic to another path. The assigned LUNs are then in­te­grat­ed and rec­og­nized by the operating system as ad­di­tion­al drives.

Step 6: Security and access control

To ensure that not every server can access arbitrary storage areas, so-called zones are set up. They define which server is allowed to access which storage resources. For iSCSI con­nec­tions, au­then­ti­ca­tion via CHAP (Challenge Handshake Au­then­ti­ca­tion Protocol) is also used.

Step 7: Testing and mon­i­tor­ing

Before the SAN is put into pro­duc­tive use, all con­nec­tions are tested. This includes checking whether the storage is ac­ces­si­ble from all des­ig­nat­ed servers and whether it au­to­mat­i­cal­ly switches to redundant systems in case of a failure. After suc­cess­ful test operation, mon­i­tor­ing is set up to con­tin­u­ous­ly supervise the condition of the hard drives, uti­liza­tion, and con­nec­tion path activity.

Use cases of Storage Area Networks

Storage area networks are primarily used in busi­ness­es that need to process and store large amounts of data, such as in data centers, with cloud providers, or in media and film pro­duc­tion. A SAN is es­pe­cial­ly suitable for en­vi­ron­ments where many servers need to access the same data si­mul­ta­ne­ous­ly, such as in database ap­pli­ca­tions, vir­tu­al­iza­tion solutions, or ERP systems. In research and science, SANs also offer crucial ad­van­tages due to their high speed and re­li­a­bil­i­ty.

In the area of data backup, the SAN serves as a powerful and scalable solution for backups and recovery. Thanks to high avail­abil­i­ty and re­dun­dan­cy, SAN is also fre­quent­ly used for business-critical ap­pli­ca­tions where a storage system failure would have severe con­se­quences. A SAN is also suitable for companies with multiple locations or dis­trib­uted data centers, as the storage can be managed in­de­pen­dent­ly of the server locations.

Overview of the ad­van­tages of Storage Area Networks

Operators of a SAN benefit from combining the ca­pac­i­ties of various physical data storages into a virtual storage foun­da­tion that is flexibly and platform-in­de­pen­dent­ly available to any number of servers. This de­cou­pling of storage medium and accessing server sim­pli­fies the man­age­ment and scaling of available storage capacity and reduces the load on the LAN. The fiber-optic-based storage area network supports high data transfer rates due to the standard interface, Fibre Channel.

Mul­ti­pathing and the cross-con­nec­tion-focused Fibre Channel fabric prevent overloads and ensure constant avail­abil­i­ty of the data stored in SAN storage. Multiple paths between the data pool and the user can always be used for access. The redundant dis­tri­b­u­tion of data across multiple physical systems guar­an­tees high security of the stored content. Delays in si­mul­ta­ne­ous data access are minimized. Due to effective storage man­age­ment, SAN storage is often used as a basis for virtual servers in the hosting business, which are offered to end customers as “In­fra­struc­ture as a Service” (IaaS) via the cloud.

Ad­van­tages of SAN at a glance:

✓ Cen­tral­ized, virtual storage base from multiple physical data carriers

✓ Flexible and platform-in­de­pen­dent access by an unlimited number of servers

✓ De­cou­pling of storage medium and server sim­pli­fies man­age­ment and scaling

✓ Relief for the LAN as the SAN operates as a separate network

✓ High data transfer rates through fiber optic tech­nol­o­gy and Fibre Channel

✓ Mul­ti­pathing allows multiple data paths si­mul­ta­ne­ous­ly and prevents bot­tle­necks

✓ High avail­abil­i­ty through in­ter­con­nec­tions in the Fibre Channel fabric

✓ Redundant data storage on multiple physical systems increases data security

✓ Min­i­miza­tion of delays during si­mul­ta­ne­ous accesses

✓ Efficient storage man­age­ment for large volumes of data

✓ Ideal for vir­tu­al­iza­tion and cloud services, e.g., for In­fra­struc­ture as a Service (IaaS)