Goswin von Brederlow wrote:
John Hughes <john@xxxxxxxxx> 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).
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