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

[Kelly Sauke <ksauke@fastenal.com>]

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�ngliche 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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