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





Fiederling, Daniel wrote:
Hi,

thank you all for your answers. I currently test a setup with md for failover.
To clarify: we have two Clariions in two different locations that are used for failover. Of course on each Clariion the disks are set up as raid 5. My question was about setting up a mirror that "copies" the data on each Clariion.
We use either Veritas Volume Manager or EMC MirrorView to accomplish this. We've had no luck in our lab getting mirrored LVM volumes to work properly.

Currently I use OpenSuSE 10.1 as distribution so unfortunately I can't use PowerPath because I only get rpms for sles or rhel that can't be installed. I know it's the wrong place for this question but: had someone success on installing PowerPath on non supported systems?
There used to be a tarball install for PowerPath. I haven't used it for about 3 years now since all we have are RHEL systems and the RPMs work fine but they might still be shipping the tarball.
Kelly, I installed a package called multipath-tools version 0.4.6 which contains multipath and multipathd by Christophe Varoqui. Is that the mpio package you mentioned?
Yes, that is the package that I was talking about.

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.

Ciao
Daniel



-----Urspr√ľngliche Nachricht-----
Von: linux-lvm-bounces redhat com [mailto:linux-lvm-bounces redhat com] Im Auftrag von Kelly Sauke
Gesendet: Donnerstag, 13. Juli 2006 20:04
An: LVM general discussion and development
Betreff: Re: [linux-lvm] SAN setup with host mirrored disks

Do the Raiding on the Clariion. Then use either PowerPath or mpio (on RHEL 4 U3 or newer) to do your failover. If you use md for your failover layer you may get IO errors on the non-active paths. You need something that is aware of the clariion setup and that would be PowerPath or the shipped mpio.

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