[lustre-discuss] poor performance on reading small files

Riccardo Veraldi Riccardo.Veraldi at cnaf.infn.it
Wed Aug 3 18:25:25 PDT 2016

MY issue is related on reading bunch of 20KB slices inside a bigger 
200GB side.
I found out it is not related to Lustre but to ZFS.
So I set up ZFS with proper record size and the problem looks like to be 
Thanks for your hints.


On 03/08/16 08:32, Mohr Jr, Richard Frank (Rick Mohr) wrote:
> Do you have the Lustre read caching feature enabled?  I think it should be on by default, but you might want to check.  If the files are only 20 KB, then I would think the Lustre OSS nodes could keep them in memory most of the time to speed up access (unless of course this is a metadata bottleneck as Oliver suggested.)  Do your OSS nodes have a lot of memory?  Do you know what your typical memory usage is on the OSS nodes?
> --
> Rick Mohr
> Senior HPC System Administrator
> National Institute for Computational Sciences
> http://www.nics.tennessee.edu
>> On Jul 28, 2016, at 10:19 PM, Riccardo Veraldi <Riccardo.Veraldi at cnaf.infn.it> wrote:
>> Hello,
>> I have a lustre cluster on rhel7, 6 OSS each of them has 3 OSTs and 1 MDS.
>> I am using lustre on ZFS.
>> While write performances are excellent also on smaller files, I find there is a drop down in performance
>> on reading 20KB files. Performance can go as low as 200MB/sec or even less.
>> I am talking about random reads and random stride reads.
>> I did the following to try to improve things:
>> 	• disabled lnet debug messages:
>> 		• sysctl -w lnet.debug=0
>> 	• increased dirty cache
>> 		• lctl set_param osc.lutrefs\*.max_dirty_mb=256
>> 	• increased number of RPC in flight
>> 		• for i in `ls  /proc/fs/lustre/osc/lustrefs-OST00*/max_rpcs_in_flight`; do echo 32 > $i; done
>> it did not improve reading 20KB file performances.
>> I have to say in advance I did not set up any striping because I will have no more than 6 concurrent reads and writes,
>> so striping is not that much important for me.
>> Here the problem is that one single random read  of a 20KB file is around 190MB/s and this is really disappointing.
>> I am open to any suggestion.
>> I made sure it is not a ZFS problem, on the OSSs ZFS is performing like a charm locally.
>> thank you
>> Riccardo
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