[Lustre-discuss] advice on OST journals in OSS failover pairs

Cory Spitz spitzcor at cray.com
Mon Feb 14 07:46:49 PST 2011


You will find that async jounral commits don't help O_DIRECT I/O though.
 So, maybe you should think about using both.

Thanks,
-Cory

On 02/13/2011 06:04 PM, Oleg Drokin wrote:
> Hello!
> 
> On Feb 13, 2011, at 6:54 PM, Samuel Aparicio wrote:
> 
>> We are planning OSS failover pairs for a lustre deployment, the question of external journals comes up.
>> testing showed that for our applications having an external journal for the OSTs provides a worthwhile increase in performance.
>>
>> For a failover pair this presumably means that the OST journals should have to reside on an external storage target that each OSSs pair can see?
> 
> Yes, basically you need two LUNs visible on both nodes per OST. One for the data and one for the journal.
> 
>> Or would the MDS journal take over in the case of an OSS switchover?
> 
> MDS journal is just for the MDS, it has nothing to do with OSTs.
> 
> Also you might want try async journal commits (+ make your journals big) to see if that improves your performance in a similar way to an external journal.
> 
> Bye,
>     Oleg
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