[DRBD-user] Question on drbdadm verify

Lars Ellenberg lars.ellenberg at linbit.com
Sat Jul 2 15:37:15 CEST 2011

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

On Fri, Jul 01, 2011 at 11:00:32PM +0200, Lionel Sausin wrote:
> Hi,
> My understanding is that "verify" has a source and a target - and then
> when you resync, blocks will flow from the source to the target, so if
> the source is corrupt you'll replicate that corruption.
> Anyone please correct me if I'm wrong.


The direction of the resync, once it happens,
has nothing to do with the "direction" of the verify.

The "diretion" of the verify is mostly an internal detail only,
of not much practical relevance.

Verify just compares checksums of blocks,
and marks blocks as being "different": out-of-sync.

Resync bases the decision on the direction on the UUIDs,
so if you have a "classic" Primary/Secondary setup,
with disk state "UpToDate" on the Primary,
then the resync direction caused by disconnect/reconnect
is always from Primary to Secondary.

> Lionel Sausin.
> Le -10/01/-28163 20:59, Dominik Klein a écrit :
> > Anyone?
> >
> > Thanks
> > Dominik
> >
> > On 06/28/2011 08:29 AM, Dominik Klein wrote:
> >> Hi
> >>
> >> while recovering from a failure that impacted a node's power and its
> >> raid controller's battery (ouch), I came across a question regarding
> >> drbdadm verify I could not find the answer to. Maybe you guys can shed
> >> some light.
> >>
> >> In my situation, drbd thinks it did write data that might not have made
> >> it to disk (read: simultaneous power and raid ctrl battery failure). I
> >> can see that the root fs misses data about 1 minute of logs, so I assume
> >> something like this for the drbd partitions as well.
> >>
> >> So, say there is a cronjob on the node that had the outage which runs
> >> drbdadm verify every day. Would blocks that changed on node2 (no outages
> >> there) in the meantime be overwritten with what is empty/bad on node1?
> >>
> >> I know it wouldn't be overwritten right away, just marked oos, but what
> >> would happen on the next disconnect/connect?
> >>
> >> Regards
> >> Dominik
> >
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: Lars Ellenberg
: LINBIT | Your Way to High Availability
: DRBD/HA support and consulting http://www.linbit.com

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