[Gluster-users] GlusterFS on high latency links

Johannes Grassler johannes at btw23.de
Tue May 26 10:38:37 UTC 2009


I'm running two GlusterFS nodes for a replicated data storage setup
trough a high latency DSL line (60-70ms RTT). File access works alright,
i.e. files are obviously accessed on the local node, but all operations
involving meta data (such as directory listings) are incredibly slow (20
seconds and more for a well-populated directory of ~200 entries).

The link is fairly low bandwith, too (128Kbit/s), but I simulated that
situation on the high bandwith link of my test setup using traffic
shaping and still got a rather snappy response. Testing happening late
yesterday night I wasn't really up to figuring out how to worsen latency
using queue disciplines. But seeing as latency is the only difference
between the test setup and the production environment (0.3-0.5ms vs.
60-70ms) it seems to be the cause of the problem.

I tried read-ahead with a cache and and the read-subvolume option, but
to no avail. Both only seem to apply to the data payload of files, i.e.
actually reading data from a file works at the speed you'd expect from
local storage but metadata access remains sluggish.

Are there any more knobs one could fiddle with to accomodate the high
latency line? If not would a reduction of the latency to 10-20ms RTT
help (the DSL lines involved could probably be switched to Fastpath



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