software raid auto assembly problem on Xen host

Nicholas Leippe nick at leippe.com
Wed Mar 3 15:07:00 MST 2010


On Wed, Mar 3, 2010 at 3:00 PM, Michael Torrie <torriem at gmail.com> wrote:
> Nicholas Leippe wrote:
>> The option you're looking for is --homehost= during array creation.
>> It affects the metadata, and depending on the superblock version you
>> chose the UUID.
>> I don't know if you can change it after-the-fact.
>> I do know that only 0.90 superblocks is supported for some operations
>> (booting off of raid1 I believe is one of them), despite the 1.0
>> version being several years old and improved in a few ways. Go figure.
>
> Unfortunately since RHEL itself made the RAID during install, who knows
> if it did the right thing with homehost or not.

You should be able to view all of the superblock metadata with examine
and/or query management flags to mdadm and see how they are
configured.

> If I read the manpages correctly, this is how you would change it after
> the fact (as an example):
>
> mdadm -A /dev/md4 --homehost=<vmhostname> --update=homehost --auto=yes
> /dev/sdd1 /dev/sdp1
>
> However this had no effect.  The host still happily assembles
> everything, even things with this new homehost.  I'm wondering if
> there's not a bug in the redhat initrd stuff.

Ah, yes. Forgot about that. Even if you tell the kernel
raid=noautodetect there may be an init script that looks for md
devices to assemble. I haven't used redhat recently enough to know.
You'll have to find it and disable it.

It might be part of the local mount (equivalent) init script.



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