[Gluster-users] URGENT - Cheat on quorum

[Ravishankar N]

On 05/22/2017 11:02 AM, WK wrote:
>
>
>
> On 5/21/2017 7:00 PM, Ravishankar N wrote:
>> On 05/22/2017 03:11 AM, W Kern wrote:
>>>
>>> gluster volume set VOL cluster.quorum-type none
>>>
>>> from the remaining 'working' node1 and it simply responds with
>>>
>>> "volume set: failed: Quorum not met. Volume operation not allowed"
>>>
>>> how do you FORCE gluster to ignore the quorum in such a situation?
>>>
>> You probably also have server quorum enabled 
>> (cluster.server-quorum-type = server). Server quorum enforcement does 
>> not allow modifying volume options or other actions like peer 
>> probing/detaching if server quorum is not met.
>>
>
> Great, that worked.  ie  gluster volume set VOL 
> cluster.server-quorum-type none
>
> Although I did get an error  of "Volume set: failed: Commit failed on 
> localhost, please check the log files for more details"
>
> but then I noticed that volume immediately came back up and I was able 
> to mount the single remaining node and access those files.
>
> So you need to do both settings in my scenario.
>
>
>> Also, don't disable client quorum for arbiter volumes or you will end 
>> up corrupting the files. For instance, if the arbiter brick was the 
>> only one that is up, and you disabled client quorum, then a writev 
>> from the application will get a success but nothing will ever get 
>> written on-disk on the arbiter brick.
>
> Yes, I am learning the pro/cons of arbiter and understand their 
> limitations.
>
> In this test case, I had taken the arbiter OFFLINE (deliberately) and 
> I was rehearsing a scenario where only one of the two real copies 
> survived and I needed that data.  Hopefully that is an unlikely 
> scenario and we would have backups, but I've earned the grey specs in 
> my hair and the Original Poster who started this thread run into that 
> exact scenario.
>
> On our older Gluster installs without sharding, the files are simply 
> sitting there on the disk if you need them. That is enormously 
> comforting and means you can be a little less paranoid compared to 
> other distributed storage schemes we use/have used.
>
> But then I have my next question:
>
> Is it possible to recreate a large file (such as a VM image) from the 
> raw shards outside of the Gluster environment if you only had the raw 
> brick or volume data?
>
> From the docs, I see you can identify the shards by the GFID
>
> # getfattr -d -m. -e hex/path_to_file/
> # ls /bricks/*/.shard -lh | grep /GFID
>
> Is there a gluster tool/script that will recreate the file?
>
> or can you just sort them sort them properly and then simply cat/copy+ 
> them back together?
>
> cat shardGFID.1 .. shardGFID.X > thefile
> /

Yes, this should work, but you would need to include the base file (the 
0th shard, if you will) first in the list of files that you're stitching 
up.  In the happy case, you can test it by comparing the md5sum of the 
file from the mount to that of your stitched file.
-Ravi
> /
> Thank You though, the sharding should be a big win.
>
> -bill/
> //
>

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