[Gluster-users] AFR: Fail lookups when quorum not met
ravishankar at redhat.com
Fri Sep 22 06:57:46 UTC 2017
In AFR we currently allow look-ups to pass through without taking into
account whether the lookup is served from the good or bad brick. We
always serve from the good brick whenever possible, but if there is
none, we just serve the lookup from one of the bricks that we got a
positive reply from.
We found a bug  due to this behavior were the iatt values returned
in the lookup call was bad and caused the client to hang. The proposed
fix  was to fail look ups when we definitely know the lookup can't be
trusted (by virtue of AFR xattrs indicating the replies we got from the
up bricks are indeed bad).
Note that this fix is *only* for replica 3 or arbiter volumes (not
replica 2, where there is no notion of quorum). But we want to 'harden'
the fix by not allowing any look ups at all if quorum is not met (or)
it is met but there are no good copies.
Some implications of this:
-If a file ends up in data/meta data split-brain in replica 3/arbiter
(rare occurrence), we won't be able to delete it from the mount.
-Even if the only brick that is up is the good copy, we still fail it
due to lack of quorum.
Does any one have comments/ feedback?
 https://review.gluster.org/#/c/17673/ (See review comments on the
landing page if interested)
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