[DRBD-user] drbdadm verify always report oos

Veit Wahlich cru.lists at zodia.de
Wed May 18 17:58:53 CEST 2016

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.


how did you configure die VMs' disk caches? In case of qemu/KVM/Xen it
is essential for consistency to configure cache as "write through", any
other setting is prone to problems due to double-writes, unless the OS
inside of the VM uses write barriers.

Although write barriers are default for many Linux distributions, it is
often disabled within VMs for performance reasons, e.g. by the
virt-guest profine in tuned.
Also Linux swap does not support write barriers at all, meaning that
migrating a VM might not cause file system inconsistencies but memory
corruptions inside a VM, leading to unpredictable results.

Windows OS is also very prone to double-write problems.

If you use any VM cache configuration other than write through, please
consider switching to write through. VMs will need to be restarted.
After all VMs have been restarted, use verify, disconnect, connect to
get rid of oos sectors and check using verify if they occur again.

When migrating VMs between hosts, you may ignore warnings stating write
through cache to be unsafe for migration.

Google for this issue for further information.

// Veit

Am Mittwoch, den 18.05.2016, 18:21 +0800 schrieb d tbsky:
> hi:
>     I am using drbd 8.4.7 which comes from epel under scientific linux
> 7.2.  when I try "drbdadm verify res", it report there is oos.
>    so I disconnect/connect the resource, the oos now becomes 0. but
> when I verify it again, it report oos again.  the oos amount is
> different than previous, but the oos sector numbers are simliar.
>    I also try "invalidate-remote" to resync all and then verify, but
> it still report oos.
>     I don't know what happened, it seems my cluster has big problems
> with data consistency. but all the vm running above the drbd resources
> seems fine, and I migrate them between hosts many times.
>    is the behavior normal or I should replace the hardware now?
>    thanks for help!!
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