[Gluster-users] [Gluster-devel] Fwd: Behaviour of simple distributed volumes on failed bricks?

[Raghavendra G]

On Thu, Jan 12, 2017 at 4:35 PM, Raghavendra G <raghavendra.hg at gmail.com>
wrote:

>
>
> On Thu, Jan 12, 2017 at 9:20 AM, B.K.Raghuram <bkrram at gmail.com> wrote:
>
>> cc'ing devel as well for some developer insight..
>>
>> ---------- Forwarded message ----------
>> To: gluster-users <gluster-users at gluster.org>
>>
>>
>> I had a question on the expected behaviour of simple distributed volumes
>> when a brick fails for the following scenarios (as in, will the scenario
>> succeed for fail) :
>>
>> - New file creation if that file name hashes to the failed brick
>>
>
> Fails
>
>
>> - New file creation if that file name hashes to one of the remaining
>> functional brick
>>
>
> Succeeds
>
> - New directory creation if that file name hashes to the failed brick
>>
>
> Fails
>
>
>> - New directory creation if that file name hashes to one of the remaining
>> functional brick
>>
>
> Succeeds. Layout is spread only to the functional bricks. Non-functional
> bricks are not part of layout of the directory. In other words files of the
> directory won't be stored in non-functional bricks
>
>
>> - File modifications/deletions if that file name hashes to the failed
>> brick
>>
>
> Fails
>

Fails mostly. However, let's say if the inode of file has been looked up
when hashed-brick was up, then operations succeed even if hashed-brick goes
down later. Following sequence of ops succeed:

1. hashed-brick up
2. Lookup (file) => success
3. open (file) => success (fd)
4. hashed-brick goes down
5. write/read (fd) => success

Note that if the inode is cached in vfs/kernel after 2, even path based
operations like stat, open, chmod etc can succeed if hashed-brick goes down
immediately after successful lookup. The point is only fresh lookups fail
if hashed brick/subvol is down.


>
>> - File modifications/deletions if that file name hashes to one of the
>> remaining functional brick
>>
>
> Succeeds
>
>
>> - Directory renames/deletions if that file name hashes to the failed brick
>>
>
> Fails
>
>
>> - Directory renames/deletions if that file name hashes to one of the
>> remaining functional brick
>>
>
> Fails
>
>
>>
>>
>> _______________________________________________
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>> Gluster-devel at gluster.org
>> http://www.gluster.org/mailman/listinfo/gluster-devel
>>
>> --
>> Raghavendra G
>>
>> <http://www.gluster.org/mailman/listinfo/gluster-devel>
>
> <http://www.gluster.org/mailman/listinfo/gluster-devel>
>



-- 
Raghavendra G
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