[lustre-discuss] poor performance on reading small files

[Riccardo Veraldi]

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:
      o sysctl -w lnet.debug=0
  * increased dirty cache
      o lctl set_param osc.lutrefs\*.max_dirty_mb=256
  * increased number of RPC in flight
      o 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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