[CentOS] mdraid on top of mdraid

Mon Mar 21 22:24:33 UTC 2011
Ross Walker <rswwalker at gmail.com>

On Mar 21, 2011, at 3:21 PM, Emmanuel Noobadmin <centos.admin at gmail.com> wrote:

>> Since your exporting the storage as iSCSI, the host machine will see
>> it as a raw disk, irrespective of how it's setup on the exported
>> server. So, yes, you can do this.
> Sorry for my ambiguity, I meant that mdadm would be on the host machine.
> e.g. Using just a 2 node, raid 1 situation
> Storage 1
> -> Disk exported on,
> Storage 2
> -> Disk exported on,
> Host
> -> mdadm multipath md0 =,
> -> mdadm multipath md1 =,
> ---> mdadm raid 1 md2 using md0 md1

Yes this will work, dm-multipath and mdraid use different subsystems.

Configure open-iscsi to log into the two targets with two sessions each, setup the dm-multipath to arrange the sessions as either a round-robin or fail-over, then create a mdraid RAID1 out of the two multipath targets (use their multipath identities not their raw identities).

There may be timing issues on system shutdown/startup, so test that fully and tweak it until it starts up properly without requiring a resync.