[Gluster-users] How to identify a files shard?

[Paul Cuzner]

Just wondering how shards can silently be different across bricks in a
replica? Lindsay caught this issue due to her due diligence taking on 'new'
tech - and resolved the inconsistency, but tbh this shouldn't be an admin's
job :(



On Sun, Apr 24, 2016 at 7:06 PM, Krutika Dhananjay <kdhananj at redhat.com>
wrote:

> OK. Under normal circumstances it should have been possible to heal a
> single file by issuing a lookup on it (==> stat on the file from the
> mountpoint). But with shards this won't work. We take care not to expose
> /.shard on the mountpoint, and as a result any attempt to issue lookup on a
> shard from the mountpoint will be met with an 'operation not permitted'
> error.
>
> -Krutika
>
> On Sun, Apr 24, 2016 at 11:42 AM, Lindsay Mathieson <
> lindsay.mathieson at gmail.com> wrote:
>
>> On 24/04/2016 2:56 PM, Krutika Dhananjay wrote:
>>
>>> Nope, it's not necessary for them to all have the xattr.
>>>
>>
>> Thats good :)
>>
>>
>>> Do you see anything at least in .glusterfs/indices/dirty on all bricks?
>>>
>>
>> I checked, dirty dir empty on all bricks
>>
>> I used diff3 to compare the checksums of the shards and it revealed that
>> seven of the shards were the same on two bricks (vna & vng) and one of the
>> shards was the same on two other bricks (vna & vnb). Fortunately none were
>> different on all 3 bricks :)
>>
>> Using the checksum as a quorum I deleted all the singleton shards (7 on
>> vnb, 1 on vng), touched the file owner and issule a "heal full". All 8
>> shards were restored with matching checksums for the other two bricks. A
>> rechack of the entire set of shards for the vm showed all 3 copies as
>> identical and the VM itself is functioning normally.
>>
>> Its one way to manually heal up shard mismatches which gluster hasn't
>> detected, if somewhat tedious. Its a method which lends itself to
>> automation though.
>>
>>
>> Cheers,
>>
>>
>> --
>> Lindsay Mathieson
>>
>>
>
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