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Re: AW: AW: [linux-lvm] SAN setup with host mirrored disks

Fiederling, Daniel wrote:
Currently I have only one path to each disk but further on I'd like to test a setup with multiple paths. But am I right that I have to use md on top of multipathd for getting the two disks mirrored?
Yes, multipathd only handles the multiple paths on a per disk basis. If you need them mirrored you have to use something on top of the multipath layer. Using md is one option that should work just fine.
I tested different qla2xxx drivers (SuSE shipped, origanal download packages from qlogic, packages from hp) and the non suse offered much more module parameters - one of them was about en-/disabling failover. I would guess that the qla2xxx driver or the card firmware can handle multiple paths. But I'm not sure about that...

I've yet to meet an HBA that doesn't work with multiple paths. I would check EMC's support matrix for your particular card. I know that we have to run specific EMC firmware on our HBAs to be fully supported. I think by running the non EMC firmware you lose some of the functionality and may run into some stability issues. I can't comment on that further since we've never done any testing with non-EMC firmware.

-----Urspr√ľngliche Nachricht-----
Von: linux-lvm-bounces redhat com [mailto:linux-lvm-bounces redhat com] Im Auftrag von Kelly Sauke
Gesendet: Montag, 17. Juli 2006 15:36
An: LVM general discussion and development
Betreff: Re: AW: [linux-lvm] SAN setup with host mirrored disks

Why do I have to expect io errors when using md? What is special about the Clariion setup? I would expect that the san disks are only "normal" scsi disks for linux...
The difference comes in how the multiple paths to the same disk are handled under linux. If you only have one path to each disk, then this doesn't apply to you. I guess I forgot to clarify if you had more than one path. Anyway, if you have multiple paths mpio knows which is the Active path and which is the Passive path. Sending IO down a passive path will result in IO errors.

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