[dm-devel] dm mirror with failed device
malahal at us.ibm.com
malahal at us.ibm.com
Tue Sep 23 16:11:26 UTC 2008
Stephen Beynon [stephen at octopus-technologies.com] wrote:
> This is probably a stupid question, in which case I apologise in advance.
>
> I am looking to set up a number of machines with internal disks mirrored onto
> an iscsi server. I aim to provide resiliance against disk failures, and the
> iscsi server will be a handy single point to backup.
>
> I set up the following test mirror.
>
> # dmsetup status mirror
> 0 16777216 mirror 2 254:8 8:16 32768/32768 0 1 core
> # dmsetup table mirror
> 0 16777216 mirror core 1 512 2 254:8 0 8:16 0
>
> As a test I shutdown the iscsi server and continued writes to the mirror
> device. As expected syslog recorded i/o errors on the iscsi lun, but writes
> to the mirror continued. After waiting a few minutes I expected to see that
> parts of the mirror were out of sync, however dmsetup status gave exactly the
> same results as above.
>
> When I restarted the iscsi server blocks started to be written to the iscsi
> server again, but the changes that happened during the iscsi server down time
> were never replicated. Clearly this left the mirror in an inconsistent state
> with the only indication of problems being in syslog.
>
> Is there any way I can configure dm-mirror to either mark the blocks as out of
> sync when a write fails, and re-try the write later ?
>
> I am currently running Ubuntu gutsy on the client machines, so it does not
> have dmeventd, but from reading the docs it it not clear that dmeventd would
> help.
What kernel version?
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