At the enterprise storage level, there's a lot more direct-attached storage (DAS) -- storage directly connected to a server instead of networked through Fibre Channel or Ethernet switches -- than you might think.
Some organizations are turning away from SANs and NAS and returning to DAS as a low-cost storage alternative for certain types of applications. For instance, Microsoft recommends DAS for Exchange to lower cost and to simplify management. Other emerging technologies are making DAS more viable by improving performance, lowering its cost and necessitating shared storage.
The bottom line: There's a lot of DAS in the enterprise. . .and a lot of application-specific servers and file servers that still have DAS."
The most common form of DAS comes from server/storage vendors, such as Hewlett-Packard and Dell. More storage-specific DAS products include entry-level configurations of IBM's DS3000, HP's MSA 2000 and EMC's Clariion AX4.
Emerging technologies, such as SAS drives, blade servers and virtual servers, make DAS more viable than it used to be by improving performance, lowering cost or necessitating shared storage. But while the perception is that DAS appeals mostly to SMBs because of cost, the reality, according to analyst Greg Schulz of the StorageIO Group, is that "there is a lot of DAS in the enterprise."
Storage directly attached to a server is how disk capacity has historically been managed. Networked storage, like SANs and NAS, has its obvious advantages, but companies often turn to it as a low-cost alternative for certain types of applications.
Microsoft Exchange 2007 is the application leading the DAS revival, which began earlier this year when Microsoft recommended that users with large mailboxes use DAS rather than networked storage to simplify management. A key feature, Cluster Continuous Replication (CCR), has been added to that version of the email application that allows Exchange to handle high-availability clustering so server nodes can have the same redundancy as SAN storage.
Read more about how DAS is catching on for database applications.
DAS is a lower-cost and easier-to-manage alternative to SAN and NAS. George Crump, founder of Storage Switzerland, an analyst firm that focuses on storage virtualization, discusses where DAS is headed and if it can really hold its own against SANs.
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