Question about HBA speeds and PowerPath

Question

Hello,

I have a Win 2k3 server with 2 HBA cards. One is a 2gb card and the other is a 4gb card. They are going into a fiber switch and then to CLARiiON AX150.

I would like to know if I'm better of having both HBA cards as active or if it is better to have the 2gb HBA as a standby?

I have been told that PowerPath will take the lowest common denominator and send data at that speed (in this case 2gb). If that is the case, I would rather only have the 4gb card active and keep the other one as standby.

Or does PowerPath aggregate the speeds? In other words, giving me 6gb when both HBA cards are set to active?

Thanks,

MacAddict1 · Answer

Glen,Thanks. The problem is that this server only has 3 PCI slots, 1 PCIe and 2 PCIx slots.I'm using a PCIx slot for a SCSI card for a LTO2 tape loader so right now I have a 4gb HBA on the PCIe slot and a 2gb HBA on the other PCIx slot.So far it seems to be working fine...Thanks

GlenH · Answer

Hi Mac,Welcome to the forum's..As a general rule, you most definitely should use both connections, and have both active - there will be no discernable difference in performance if both connections are running at 2Gb or 4Gb, however you will unbalance the array if you only have 1 path active.In reality, only high end servers and storage platforms can push a single channel above 2Gb (and even then only with very large I/O sizes) - for most environments you only see the benefit of 4Gb with ISL's between switches and not for the Host or storage port connections.All that being said - for powerpath configurations, we actually only support connections to a single LUN through identical HBA's, so really, you should try and get another HBA to match either of the ones you already have... (as per emc79064 and the Powerpath Product Guide) so that you have 2 identical HBA's in that server.Hope that helps,Glen.

dynamox · Answer

Glen,so if somebody would install Qlogic and Emulex in the same box and zone it to the same storage array/LUN ...PowerPath would only select one hba to use ..even though both are fiber channel HBAs ?Thanks

GlenH · Answer

Dynamox / Mac,Powerpath seems to function across different HBA's - it's technically not supported but i've seen it work.If you must do it (not that i'm saying you should), I would highly recommend that the HBA's at least use the same driver (easy enough for emulex) - doing one path lpfc and the other qla sounds evil and i wouldn't like to be calling EMC support with that configuration as you know what they're going to say...Mac - for your config, it's a little tough with the slots you have... I don't have a good answer for you.. Sorry.Glen.

dynamox · Answer

i was just curious if it would work ..not that i would do it in production ..but maybe in the lab in case two identical manufactured HBAs are not around.

Allen Ward · Answer

Hi Mac,Another option you may want to consider (to be in a more supportable state) is a dual headed HBA. Personally I don't like them because they don't give the real redundancy of separate physical components, but my server team likes to use them, and I'm only accountable for High Availability from the cables plugged into the HBA(s) on the array. As long as the server gives my dual ports one way or another, I'm happy.Just my two cents worth though...

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Question about HBA speeds and PowerPath

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