[Gluster-users] URGENT - Cheat on quorum

[WK]

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

Thank You though, the sharding should be a big win.

-bill/
//

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