Servers meet storage, virtually


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Simpler SAN management
Virtual machines break the "one application, one server" mentality and let you collapse multiple physical servers into one, says Rob Peglar, CTO at SAN array vendor Xiotech Corp. As a result, the number of server-to-storage connections an administrator needs to manage goes down. When 10 physical servers are collapsed into a single large one, "instead of having ten different zones to configure and manage, you have one," says Peglar.

Having fewer physical connections to manage has economic ramifications too. With fewer servers, you have fewer host bus adapters (HBAs) and switch ports to purchase and manage. And those savings can be applied to putting servers on the SAN that previously could not be cost-justified.

Oak Associates, for one, has seen utilization of the firm's expensive Symmetrix skyrocket since VMware was put in place. "EMC told us that we would get server consolidation benefits out of our SAN, but we never really saw that," says Hill. "Now, with VMware, we are."

Mike Karp, senior analyst with Enterprise Management Associates, an analyst firm in Boulder, CO, thinks you can take virtualization one step further, and use virtualized storage for your virtual servers. "It makes sense. If you're doing one, why not try the other?" With virtualized storage, like virtual servers, "you can squeeze every last nickel of value out of the hardware," Karp says.


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In most VMware environments, SANs are not required, says Raghu Raghuram, VMware's director of product management, although, "we do recommend a SAN for VMotion," which is software that lets you move a virtual machine to a different physical host while it is running. In that case, a SAN allows you "to take individual servers and turn them back into the compute pool."

VMware's indifference to whether or not a SAN is present has a lot to do with VMware ESX Server File System (VMFS), the clustered file system that's part of ESX Server. What VMFS does, Raghuram explains, is "provide a level of indirection between the virtual machines and the actual storage." From a virtual machine's perspective, "all you see is a SCSI disk," while VMFS "takes care of communicating with the SAN" or the local storage.

This was first published in July 2004

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