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)