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Re: [Xen-users] MD/EVMS on domU?

Andy Repton wrote on 12/12/2005 04:16:33 PM:

> Hi,
> I'm starting out with xen by trying to convert my existing gentoo
> server to be a domU under a newly created gentoo dom0.
> I have the dom0 running nicely and have most of the domU up, but the
> original server had an md/evms setup for home etc. I thought I could
> export the block devices to the domU and have md pick them up, but it
> is failing to do so. It writes
> md: Autodetecting RAID arrays.
> md: autorun ...
> md: ... autorun DONE.
> to the console, but there is nothing in /proc/mdstat nor does evms
> find the RAID or setup /dev/evms/ nodes.

First off, do not have both RAID autodetect and EVMS discover your RAID
arrays.  (That restriction needs to be noted more prominently in the EVMS
docs.) They conflict with each other.  Either disable RAID autodetect (use
fdisk's "t" command to change the partition types to 83 (Linux)) and let
EVMS discover the arrays, or disable RAID support in EVMS by deleting the
md-*.so plug-in in /lib/evms/<version>/.  If you disable RAID support in
EVMS you will have to use the RAID tools separately to manage the arrays
and EVMS to manage the rest of the devices, which kind of defeats the
purpose of EVMS to be the one place to go for all your volume configuration

> Before I waste time trying to get this up and running; is it possible
> to run MD/EVMS on a domU?

Off hand I don't see any reason why you should not be able to use MD RAIDs
and EVMS in a domU.  You should be able to apply the instructions at
http://evms.sourceforge.net/convert.html to the disk(s) being used in the
domU.  Any kernel patches you want would be applied to the domU kernel.
You should be able to skip the updates to the boot loader (step 8) since
dom0 does the booting of the domU.  All the other steps you should be able
to do within the domU once it is booted.

> I have not compiled MD or EVMS into the dom0 kernel, so that it
> doesn't try to build the RAID.

You should not need MD or EVMS in the dom0 kernel.  dom0 just serves up the
devices to the domU.  The domU then determines how it wants to use them.

Steve D.

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