Could you tell me about NAS head devices that provide a file system view of SANs? Is there any other way to achieve SAN/NAS integration? Who are the best suppliers in this regard and what are the price ranges like? How much sense does it make to go in for such a device rather than say, NetApps NAS appliances?
NAS devices that provide a file system view of a SAN are really just the NAS controller that is sometimes called a head or gateway with the storage being attached via the SAN. This is relatively simple to understand once you grasp that a NAS device has a control function (the controller or head) and a storage element. There's no difference in the storage attached as far as the code in the NAS device can tell - it's just blocks of data accessed with SCSI commands typically. By using the storage in a SAN rather than direct attached, the NAS controller has a LUN (or LUNs) assigned to it that it owns and controls as if it were direct attached. The value here is in the ability to use possibly less expensive storage in the SAN and centralize the administration of that storage (and achieve greater economies of scale).
There are other approaches being used to capitalize on SAN storage with file access that you would use for NAS: one is with a Metadata Server approach where the metadata server controls access to the storage but data is actually accessed in blocks across the SAN. This approach is used in the IBM SANergy product and EMC Highroad among others. Another approach is to create a SAN file system that treats all the storage in the SAN as if it were a very large file system (which requires sharing of information among servers). This approach is being used by a few vendors including VERITAS.
It is not appropriate to comment on who is the best vendor (that is very subjective) or the prices since the prices depend greatly on the deal you make.
The bottom line in choosing these combined NAS and SAN solutions is economics. You'll need to look at your individual situation and consider product costs, administration costs, the cost associated with your storage demand growth (how well you scale), etc. and determine the best economic answer for you. Despite what a vendor may tell you, it's not always the same solution for everyone. That's what makes it interesting.
Evaluator Group, Inc.
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This was first published in October 2001