Storage Pipeline: How to Build an iSCSI Disk Array

Posted by Howard Marks on June 2, 2006

Ideally, we'd all have all the top-shelf enterprise-class storage we need--not just for critical production apps but for development, testing, disk-to-disk backup and our disaster-recovery hot site. But real-world budgets mean we sometimes must make do with less powerful or second-hand storage.

If you have a spare server and an SCSI cabinet in your IT boneyard, you can turn them into an iSCSI disk array by adding an inexpensive iSCSI target program. Even if you have to buy the pieces, you can put together a 2-TB array for about $4,000 (see "We Built It, But Would We Buy It?"). Your new iSCSI array will be running on top of a Windows or Linux OS, so you can allocate space on your new server to file service as well as iSCSI logical drives.

You also can use this array as a stopgap. When a state agency was waiting for approval to purchase a new disk array, its Exchange servers began running short of space. The agency used a server, a SCSI cabinet and a downloaded copy of WinTarget to add storage to the servers overnight.

Maybe building an iSCSI disk array out of a server seems wacky. But many of the iSCSI disk arrays on the market, including those from well-known vendors like LeftHand Networks and MPC (formerly MicronPC), use standard Xeon motherboards. Naturally, a server-based array won't have redundant disk controllers, but the combination of a good RAID controller and iSCSI target software can produce an iSCSI array that performs as well as name-brand arrays.

Once you add iSCSI target software to a Windows or Linux server, you can create logical disks or LUNs (logical unit numbers). Most folks with enterprise arrays will create RAID sets and then slice them into LUNs to present to their servers, but having access to the underlying OS gives you more flexibility. Most iSCSI target software will let you create virtual LUNs as file objects in an existing file system on your server, or turn a volume, partition or other unformatted disk space into a LUN.