Making the most of DAS
 
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Recently, a reader asked about alternative storage solutions that use idle disk space on existing direct-attached storage. Given that there is a huge installed base of DAS devices already a part of IT infrastructures, how can companies utilize their current assets in a more flexible and balanced way?
The primary constraint to sharing storage that is directly attached to a server is that if that server for whatever reason is not functioning, the path to the shared resource will not function.
This is the reason so much work is being done to create networked storage. The fact that a network is the primary conduit of information automatically provides the customer routing options not available with a server-based infrastructure, unless clustering is implemented. Most companies are willing to incur the expense of clustering for business-critical applications, but not for all their servers. The network is an infrastructure that lends itself easily to alternate paths for failover scenarios.
What IT professionals can do with legacy DAS is to place it on the network. There are bridge devices available from companies such as Crossroads, which will allow SCSI devices to attach to a network infrastructure. The bridge will create some latency due to the translation of Fibre Channel blocks into SCSI blocks, causing some performance degradation. However, this may serve as a transition capability to allow current resources to be used in the new networked infrastructure.
The ability to use existing assets within a new infrastructure is not to be taken lightly. The costs to transition to new technology and a new infrastructure may be prohibitive for many companies. Bridges can allow the infrastructure transition to leverage existing devices for a more cost-effective solution.
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Anne Skamarock is senior analyst with Enterprise Management Associates in Boulder, Colo., an analyst and market research firm focusing exclusively on enterprise management. She can be reached via e-mail.
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