You've probably heard a lot about SANs in recent months—how centralizing storage in a single array on your network can lower overall storage costs and increase efficiencies by letting you add capacity as needed. A SAN might sound like a good idea, except for the high price tag. Converting from DAS to a SAN would require a significant up-front technology investment, not only in the storage array itself but also in Fibre Channel SAN switches and host bus adapter (HBA) cards for the array and the servers it's connected to.
But the emergence of iSCSI SAN technology about 3 years ago, along with ongoing improvements in the disk capacity, performance, and storage-management capabilities of iSCSI storage arrays, has largely eliminated cost as an obstacle to implementing a SAN. An organization can use its existing IP networking equipment to set up a storage array that supports an iSCSI connection. Furthermore, iSCSI SANs, unlike their Fibre Channel counterparts, impose no physical limitations on the distance between the array and the Ethernet switch that connects it to the network. Microsoft is also doing its part to promote iSCSI SAN technology in the Windows world—for example, by partnering with storage vendors such as EqualLogic and LeftHand Networks in its Simple SAN initiative and offering the Microsoft iSCSI Software Initiator support software.
As the buyer's guide table on page 30 shows, you can buy an iSCSI storage array for as little as around $2000— a technology investment cost that's low enough even for a small business to justify trying out iSCSI SAN technology in a test environment before making a commitment to moving production data onto a SAN or discarding DAS completely. In short, if you've been thinking about setting up a SAN for the first time, whether your organization is large or small, iSCSI is the SAN technology you'd want to use.
Storage vendors and industry analysts have historically tended to peg iSCSI SANs as a low-end storage technology offering budget-priced products that skimped on features and performance. Fortunately for IT pros, that trend is changing. Today's iSCSI storage arrays—even the lowest-priced offerings—offer standard features such as support for data snapshots, storage-management software, hot-swappable components that can be switched out quickly—in some cases, without taking the storage server down—and failover and redundancy support. Such features mean that applications that access data on the SAN experience minimal downtime due to disk failure. Furthermore, vendors are increasingly building more intelligence into their products—for example, by including RAID controllers, firmware, or storage management software—to make configuring and managing the SAN easier for administrators.
iSCSI storage arrays differentiate themselves primarily by cost and the base disk capacity and total disk capacity they support (i.e., scalability). As mentioned, you can buy an iSCSI array such as Adaptec's Snap Server 4200, which comes with 320GB of base disk capacity, for as little as $2000. Or you can spend well over $100,000 for an enterprise-class array such as Network Appliance's NetApp FAS900, comprising eight drives and providing 540GB of base capacity. The bulk of iSCSI storage arrays are priced between $4000 and $30,000, with an average price of about $20,000.
Another differentiator is data-snapshot support. Although most of the products in the buyer's guide include some type of support for data snapshots, few support Micro-soft Volume Shadow Copy Service (VSS), the snapshot capability that's built into the Windows OS.
iSCSI SANs provide an affordable way for businesses to get acquainted with the benefits of centralized storage. If you want to find out more about iSCSI SAN technology, check out the sidebar "Selecting a Storage Array for a SAN," January 2006, InstantDoc ID 48485 (part of Mel Shum's SQL Server Magazine article "SQL Server on a SAN," InstantDoc ID 48486) and Paul Robichaux's Web-exclusive series "Exchange and SANs: No Magic Bullet," parts 1 and 2, August 2005 (InstantDoc IDs 47322 and 47418, respectively).