From mboxrd@z Thu Jan 1 00:00:00 1970 From: John Hughes Subject: Re: Using linux software raid (mdadm) in a shared-disk cluster. Date: Thu, 23 Apr 2009 11:22:25 +0200 Message-ID: <49F03351.3090301@Calva.COM> References: <49E45044.5000406@Calva.COM> <87prf5m5kt.fsf@frosties.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <87prf5m5kt.fsf@frosties.localdomain> Sender: linux-raid-owner@vger.kernel.org To: Goswin von Brederlow Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids Goswin von Brederlow wrote: > John Hughes writes: > >> I've got a little shared disk cluster (parallel SCSI, external DELL >> PV210 disk cabinet). >> >> I've used linux raid to make a nice RAID10 on the external disks. >> >> I can access this from either machine in the cluster, only one at a >> time of course, it works very well and I'm happy. >> >> Now I'm running XEN and I want to be able to migrate a XEN domU from >> one machine to the other while the domU is using the RAID10 device. I >> can make this "work" using XEN's migration hooks - it calls a script >> when it has stopped the running domU and I can start the raid device >> on the destination node, ready for the arrival of the domU. >> >> There is one small problem - I can't stop the RAID10 on the source >> node until the domU has finished, so it seems to me there is a window >> that could lead to data corruption: >> > > Can you put it into read-only mode? > How do I do that? Ah, by "mdadm --readonly"[*]. > I'm not even sure putting a raid in read-only mode will stop > background syncing. > Hang on a sec, I'll try it. ... run bonnie on mounted /dev/md0, kill it, umount the device ... # cat /proc/mstat Personalities : [raid10] md0 : active raid10 sda3[0] sde2[4](S) sdd3[3] sdc3[2] sdb3[1] 32067456 blocks 64K chunks 2 near-copies [4/4] [UUUU] bitmap: 66/123 pages [264KB], 128KB chunk # mdadm --readonly /dev/md0 # cat /proc/mdstat Personalities : [raid10] md0 : active (read-only) raid10 sda3[0] sde2[4](S) sdd3[3] sdc3[2] sdb3[1] 32067456 blocks 64K chunks 2 near-copies [4/4] [UUUU] bitmap: 66/123 pages [264KB], 128KB chunk ... wait a bit # cat /proc/mdstat Personalities : [raid10] md0 : active (read-only) raid10 sda3[0] sde2[4](S) sdd3[3] sdc3[2] sdb3[1] 32067456 blocks 64K chunks 2 near-copies [4/4] [UUUU] bitmap: 0/123 pages [0KB], 128KB chunk No, it seems to keep on syncing. Bummer. > As an alternative approach how about running the raid10 inside the > domU? > Didn't want to do that as it requires exporting loadsa devices to the domU instead of one. But maybe it's the only way (without hacking the md code).