>
> Say I think my cephfs is slow when I rsync to it, slower than it
used
> to be. First of all, I do not get why it reads so
much data. I
assume
the file
attributes need to come from the mds server, so the rsync
backup should mostly cause writes not?
Are you running one or multiple MDS? I've seen cases where the
synchronization between the different MDS slow down rsync.
One
The problem is that rsync creates and renames files a
lot. When doing
this with small files it can be very heavy for the MDS.
Strange thing is that I did not have performance problems with luminous,
after upgrading to nautilus and enabling snapshots on a different tree
of the cephfs. Rsync is taking 10 hours more.
There is also another option, degrading performance on the source.
However it is impossible for me to verify this.
I have increased the mds_cache_memory_limit from 8GB to 16GB, see
what that brings.
> I think it started being slow, after enabling snapshots on the file
> system.
>
> - how can I determine if mds_cache_memory_limit = 8000000000 is
still
> correct?
>
> - how can I test the mds performance from the command line, so I can
> experiment with cpu power configurations, and see
if this brings a
> significant change?
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