[lustre-discuss] a question about max_create_count

[Andreas Dilger]

Kurt,
To clarify a bit further, the max_create_count is the maximum number of objects that the MDS might precreate in a batch on an OST if it has a high create rate.  They are not necessarily _simultaneous_ creates.

In the recent IO-500 run, Cambridge sustained 1.78M creates/sec for 5 minutes (on 24 MDTs + 24*11 OSTs, mind you), so this is not a very high limit.

On Jun 20, 2019, at 10:09, Degremont, Aurelien <degremoa at amazon.com> wrote:
> 
> Hello Kurt,
>  
> max_create_count is a tunable per OST. It controls how many object pre-creations could be done on each OST, by the MDT. If you set this to 0 for one OST, no additional object will be allocated there and no new file will have file stripes on it.
>  
> With the appropriate hardware, Lustre can create much more than 20,000 files simultaneously.
>  
> Aurélien
>  
> Kurt Strosahl <strosahl at jlab.org> wrote on 2019-06-19 at 22:43:
>>  
>> Good Afternoon,
>>  
>>     I'm in the process of testing a new lustre file system at 2.12, and in going through the documentation I saw that to stop writes from going to the system we now set the max_create_count to 0 on the mdt.
>>  
>>    I looked at that value on my system and the default seems to be 20000, am I correct in thinking that this is the maximum number of simultaneous creates that can happen on an OST?
>>  
> 

Cheers, Andreas
--
Andreas Dilger
Principal Lustre Architect
Whamcloud