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I am trying to compare VMware's new VSA with the HP LeftHand VSA. Both products allow you to run the SAN node as a VM. Reading VMware's documentation I get the impression that VMs on the same host as the SAN node access data from that node at local storage speeds, while I get the impression with HP's VSA that it presents as iSCSI and thereby subject to that slow down.

I like the HP VSA because it would allow us more than 3 nodes and it allows the migration to hardware based SAN or even mixed hardware and VM based nodes, but if I am understanding the performance difference with VMware's product I would consider that a greater value and worth the 3-node limit.

My question is with HP LeftHand VSA, since you configure targeting the cluster and not the node, will it not be able to bi-pass the artificial performance ceiling of the virtualized switch and NIC in the communication chain between the local VM and local virtual SAN node?

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Using the iSCSI protocol, the Lefthand VSA will add some latency to any disk IO requests processed through it. Unless you're looking for a high performance solution, this shouldn't be noticeable compared to the latency of the storage medium however. If you're looking for some sort of high performance solution, a VSA is probably the wrong way anyhow.

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Am I thinking about this in the wrong way? iSCSI would be limited to the 1 Gb speed of the NIC where as local IO would be limited to the 6 Gb speed of the disk. Not to mention the additional overhead of TCP. That seems like a difference that I would expect to notice. Am I over simplifying or missing a major point? – Dennis Allen Sep 27 '11 at 16:16
Local traffic doesn't actually hit the NIC. This is true of almost all networks stacks on almost all operating systems. – Chris S♦ Sep 27 '11 at 17:30
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HP suggest using up to 8 teamed GbE NICs between a pair of servers running VSA. That will cost something, but still be cheaper than a physical SAN. – Terence Johnson Feb 7 at 23:08
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