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

[Raghavendra G]

On Thu, Jan 12, 2017 at 4:44 PM, Raghavendra G <raghavendra.hg at gmail.com>
wrote:

>
>
> 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.
>

Sorry, I forgot to mention that this can happen only if actual file
(data-file) is stored on non-hashed brick and hashed-brick contains a
linkto file. If data-file is present on hashed brick and it goes down,
access fails always.

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
>>
>>
>>>
>>>
>>> _______________________________________________
>>> Gluster-devel mailing list
>>> 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
>



-- 
Raghavendra G
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