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I recently tried to sell the idea of multipathing one of our production databases (thanks to Brent at SQL Pass summit!) currently using just 1 database file (189GB!!!) on a physical server with 2 lines to a HP LeftHand P4000 SAN (via switches etc). One of the arguments against doing this was that the two lines out of the SAN are currently bonded, providing 2 x 1Gbps r/w capability to and from the SAN. The SAN admin wasn't prepared to separate the lines, partly due to other VMs on the server using them and the unknown impact any separation might have. I struggled to articulate the benefits of multipathing the database in the face of this - are there any benefits that m/p would bring versus bonded connections?

Derek Colley
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  • Your question is confusing because generally we talk about bonding for Ethernet and multipathing for SAN (FC/iSCSI). You have 2x 1Gbps links - are those one 1Gb FC or 1Gb Ethernet? If so are you using FCoE? Something about the way you have described your setup doesn't make sense. If you can clarify I think it would help. – Jeremy Oct 02 '11 at 15:03

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I'm not sure what you mean by bonding in context of SAN.

Multipathing in SAN is done first of all for RAS. You usually have paths to the LUN independent. That means different FC cards, different fabrics, different storage controllers. If your storage supports active/active operation, then you also get to use bandwidth of both links (you can issue requests in parallel over both of them).

If your storage does not support active/passive operation, then using multipathing means that you'd loose half the bandwidth, as you'll be able to talk to the LUN over one link at any given time.

However, loss of throughput (if any) is, in my opinion, more than acceptable, given increased availability. You eliminate storage-side SPOFs that way and e.g. can stagger SAN firmware upgrades / zoning changes, without risking impacting production (if after upgrade the FC switch goes haywire you can just switch to the other fabric while SAN folks execute recovery strategy).

Paweł Brodacki
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