The simplest way to explain a SAN is to compare it to a popular IT infrastructure solution — the local area network (LAN), which enables multiple PCs to share key IT resources such as applications, servers, shared files and printers. SANs provide similar resource sharing but are specifically designed to share storage devices such as disk arrays or tape libraries. The following figure illustrates a typical SAN configuration.
As this image shows, there are five basic components in a SAN:
1. Servers |
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Multiple servers and workstations from different vendors, running different operating systems, can all be connected to a SAN. Servers with a fibre channel SAN connection require a special FC card called a host bus adaptor (HBA) in each connected server. In an IP SAN, you can use a standard Ethernet NIC.
2. SAN infrastructure |
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The SAN infrastructure (fabric) includes the hardware, cabling, and software components that enable data to move into and within the SAN. HBAs and fibre-channel switches form the foundation, enabling servers and other storage devices to connect to one another.
Switches can detect failed or congested connections and intelligently reroute data to the correct device. When linked together (cascaded), switches increase the number of available SAN connections, which provides greater performance and resilience against individual connection failures. Servers can be connected to a SAN with either a single or dual connection. A dual connection gives you a fallback should one connection fail.
3. Disk storage |
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A disk array can be seen as a centralized storage pool for servers. Data from multiple servers is stored in dedicated areas called logical unit numbers (LUNs), and can be protected against data loss in the event of multiple disk failures using RAID protection. Redundant array controllers assure that servers can access their data, even if one controller or network connection fails. In addition, the modular design of disk storage allows you to grow capacity as you require.
4. Tape storage |
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Within a SAN, any disk storage (whether it‘s an external disk array or internal to the server) can be backed up directly to a tape library. This provides a fast and dedicated pathway for data backup, and frees the corporate LAN to perform its primary functions with greater efficiency.
Due to their lower network speeds, IP SANs should preferably pass data traffic through a backup server to a direct-attached tape library. Tape-based backup can be combined with disk-based backup — e.g., via a Virtual Library System (VLS) — to improve recovery processes and optimize slow server backups.
5. Management software |
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Although it is often overlooked, management software is perhaps the most important part of any SAN. Management software:
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Helps you configure and optimize individual components of the best setup. |
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Monitors the entire network for performance bottlenecks and areas of potential failure. |
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Automates time-consuming tasks such as data backup. |
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Provides usage statistics that enable you to cross-charge SAN users. |
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Virtualization functionality allows you to manage all available storage as one virtual pool, regardless or where it‘s located. |
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» Next: HP SAN technologies
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