Hi,
we are using cephfs with currently about 200 million files and a single
hosts running nightly backups. This setup works fine, except the cephfs
caps management. Since the single host has to examine a lot of files, it
will soon run into the mds caps per client limit, and processing will
slow down due to extra caps request/release round trips to the mds. This
problem will probably affect all cephfs users who are running a similar
setup.
Are there any tuning knobs on client side we can use to optimize this
kind of workload? We have already raised the mds caps limit and memory
limit, but these are global settings for all clients. We only need to
optimize the single backup client. I'm thinking about:
- earlier release of unused caps
- limiting caps on client in addition to mds
- shorter metadata caching (should also result in earlier release)
- anything else that will result in a better metadata throughput
The amount of data backed up nightly is manageable (< 10TB / night), so
the backup is currently only limited by metadata checks. Given the trend
of growing data in all fields, backup solution might run into problems
in the long run...
Best regards,
Burkhard Linke
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