[Lustre-discuss] un-even distribution of data over OSTs

Roland Laifer roland.laifer at kit.edu
Wed Mar 7 08:33:56 PST 2012


I recently had a similar problem: Very bad OST space occupation but I could not 
find a corresponding very large file. 

Finally I found a process with parent 1 that was still appending data to a 
file which was already deleted by the user, i.e. this was the reason why 
I could not find a corresponding large file with "find". 

I found that process because the corresponding client was reporting 
"The ost_write operation failed with -28" LustreError messages and because 
I was lucky that only few user processes were running on that client. 
The owner of that process had Lustre quotas of 1.5 TB but "du -hs" on his 
home directory only showed 80 GB. After killing the process Lustre quotas 
went down and "lfs df" showed that OST usage was going down, too. 


On Wed, Mar 07, 2012 at 07:41:28AM -0800, Grigory Shamov wrote:
> Dear Lustre-Users,
> Recently we had an issue with file data distribution over our Lustre OSTs. We have a Lustre storage cluster here, of two OSS servers in active-active failover mode. The version of luster is 1.8, possibly with DDN patches. 
> The cluster has 12 OSTs, 7.3Tb each. Normally, they are occupied to about 60% of the space (4.5Tb or so); but recently, one of them got completely filled (99%) with two other also keeping up (80%). The rest of OSTs stayed at the usual 60%. 
> Why would that happen, shouldn't' Lustre try to distribute the space evenly? I have checked the filled OSTs for large files; there were no files that can be called large enough to explain the difference (with size of the order of magnitude of the difference between 99% and 60% occupation, i.e. 2-3Tb); some users did have large directories, but the files were of about 5-10Gb size.
> I have checked our Lustre parameters, the qos_prio_free seems to be default 90%, qos_threshold_rr is 16%, and stripe count is 1. 
> Could you please suggest what might have caused such behavior of Lustre, are there any tunables/better values of tresholds, etc. to change to avoid such imbalances, etc.? 
> Thank you very much in advance!
> --
> Grigory Shamov
> HPC Analyst,
> University of Manitoba
> Winnipeg MB Canada
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Karlsruhe Institute of Technology (KIT)
Steinbuch Centre for Computing (SCC)

Roland Laifer
Scientific Computing and Simulation (SCS)

Zirkel 2, Building 20.21, Room 209
76131 Karlsruhe, Germany
Phone: +49 721 608 44861
Fax: +49 721 32550
Email: roland.laifer at kit.edu
Web: http://www.scc.kit.edu

KIT – University of the State of Baden-Wuerttemberg and 
National Laboratory of the Helmholtz Association

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