MDS Stability with lots of CAPS

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Hi,

According to [1] there are new parameters in place to have the MDS
behave more stable. Quoting that blog post "One of the more recent
issues weve discovered is that an MDS with a very large cache (64+GB)
will hang during certain recovery events."

For all of us that are not (yet) running Nautilus I wonder what the best
course of action is to prevent instable MDS during recovery situations.

Artificially limit the "mds_cache_memory_limit" to say 32 GB?

I wonder if the amount of clients is of influence in a MDS being
overwhelmed by release messages. Of are a handfull of clients (with
millions of CAPS) able to overload an MDS?

Is there a way, other than unmounting cephfs on clients, to decrease the
amount of CAPS the MDS has handed out, before an upgrade to a newer Ceph
release is undertaken when running luminous / Mimic?

I'm assuming you need to restart the MDS to make the
"mds_cache_memory_limit" effective, is that correct?

Gr. Stefan

[1]: https://ceph.com/community/nautilus-cephfs/


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