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Old 03-30-2010, 05:07 AM
Kiyoshi Ueda
 
Default RHEL 5.4 multipath doesn't handle virtio block devices

Hi Martin,

On 2010/03/30 10:16 +0900, Martin Schwenke wrote:
> multipath in RHEL 5.4 doesn't handle virtio block devices. It excludes
> them because they use a sysfs bus that is not recognised.
>
> Here's a patch that seems to fix this:

Why do you want to use dm-multipath on virtio block devices?

Thanks,
Kiyoshi Ueda

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Old 03-30-2010, 07:16 AM
Hannes Reinecke
 
Default RHEL 5.4 multipath doesn't handle virtio block devices

Martin Schwenke wrote:
> On Tue, 30 Mar 2010 14:07:02 +0900, Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
> wrote:
>
>> Why do you want to use dm-multipath on virtio block devices?
>
> For consistency rather than failover... :-)
>
> I'm using virtual machines to test a clustered NAS environment. The
> production setup expects to see dm devices from dm-multipath. So I'm
> using dm-multipath on virtio block devices to simulate use of
> dm-multipath in a SAN environment.
>
megasas megasas megasas ...
I posted a megasas HBA emulation for KVM a while back.
Would solve your problem rather elegantly.
But then you'd have to recompile KVM, at which point you could include
the SCSI emulation as well ...

> The RHEL 5.4 version of KVM doesn't contain a SCSI emulation, so the
> only 2 choices for large numbers of block devices are virtio and
> iSCSI. I'm trying to keep my options open for both of these.
>
> The fix for virtio block devices seems quite straightforward, so I
> thought I would propose it. :-)
>
Problem is, though, that you don't have a unique ID for virtio devices.
EG scsi_id and friends don't work here.
And AFAIR there is no feature flag which would allow you do set one.

How do you distinguish between, say, 2 virtio devices across 2 paths?

Cheers,

Hannes
--
Dr. Hannes Reinecke zSeries & Storage
hare@suse.de +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: Markus Rex, HRB 16746 (AG Nürnberg)

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