On 2018-02-12 11:39, Ellis H. Wilson III wrote:
On 02/12/2018 11:02 AM, Austin S. Hemmelgarn wrote:
BTRFS in general works fine at that scale, dependent of course on the
level of concurrent access you need to support. Each tree update
needs to lock a bunch of things in the tree itself, and having large
numbers of clients writing to the same set of files concurrently can
cause lock contention issues because of this, especially if all of
them are calling fsync() or fdatasync() regularly. These issues can
be mitigated by segregating workloads into their own subvolumes (each
subvolume is a mostly independent filesystem tree), but it sounds like
you're already doing that, so I don't think that would be an issue for
you.
Hmm...I'll think harder about this. There is potential for us to
artificially divide access to files across subvolumes automatically
because of the way we are using BTRFS as a backing store for our
parallel file system. So far even with around 1000 threads across about
10 machines accessing BTRFS via our parallel filesystem over the wire
we've not seen issues, but if we do I have some ways out I've not
explored yet. Thanks!
For what it's worth, most of the issues I've personally seen with
parallel performance involved very heavy use of fsync(), or lots of
parallel calls to stat() and statvfs() happening while files are also
being written to, so it may just be the way you happen to be doing
things just doesn't cause issues.
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