[Lustre-discuss] change raid5 to raid6 using lustre kernel

[Andreas Dilger]

On 2010-07-26, at 12:33, Brock Palen wrote:
> I know the lustre kernel has some patches to MD in there.
> We have some x4500 and x4540 that we run lustre 1.6.x on as servers.  We currently use raid5 plus spares.  We were wondering about reshaping them into raid6 by taking in the spare.
> 
> Reading online this appears doable with recent version of mdadm which because we are on rhel4 for servers we do not have.  I didn't know if this ability was in the lustre kernel, if we build the newer mdadm.

I don't think that our RAID patches take out any functionality, but we have never tested this.  I also have no idea about whether the newer mdadm has all of the functionality in the kernel that it needs, unless you are taking the Lustre RHEL5 kernel + RHEL5 mdadm, and just have RHEL4 userspace.  That would hopefully be OK, since I doubt if mdadm cares about anything else in userspace, just the kernel.

I'd be sufficiently leery of this (even w/o Lustre patches involved) that I'd make a backup of each OST before starting the reshaping.  That way, you don't need to have a backup of the whole filesystem at one time, just the one or two OSTs that are currently undergoing reshaping.

Cheers, Andreas
--
Andreas Dilger
Lustre Technical Lead
Oracle Corporation Canada Inc.