[OpenAFS] need help tuning openafs

Wes Chow wes@woahnelly.net
Fri, 3 Sep 2004 22:04:51 -0400

> >>>>I'm playing with a few of the 45 gig machines now and I've noticed
> >>>>that afsd startup times are unacceptably long.  I took the advice from
> >>>>the AFSLore wiki and used "afsd -chunk 17", however just starting afsd
> >>>>on a clean /var/cache/openafs directory takes 20-30 minutes.  On an
> >>>>already populated cache directory, it takes maybe 3 or 4 minutes.
> >>>>After it's done, afs_cachetrim runs 80-90% cpu for an unkown period of
> >>>>time.  (I have yet to see one finish, and it's been close to 2 hours).
> >>>
> >>>It has to populate the cache, the first time, and scan it on subsequent
> >>>boots, and presumably whichever filesystem you're using for the cache has
> >>>slow access times.
> >>
> >>Is the subsequent scanning what afs_cachetrim does?  The second time
> >>it boots, afsd only takes a few minutes to start so it's not so bad.
> >>What's really killing me is the fact that afs_cachetrim hasn't
> >>finished yet and is hogging so much CPU.
> subsequent boots are not subsequent scanning. subsequent boots are boots 
> after the one where you created the cache from scratch.
> >>Is the time it takes to finish proportional to the number of chunks?
> >>I've even tried chunk sizes of 2^30, but that doesn't seem to make
> >>much difference...
> afsd startup should take time proportional to the number of files it has 
> to play with (create or stat) on the way up. bigger chunksize equals fewer 
> files for a cache of the same size (unless you override the number of 
> cache files by afsd switch)

Okay, the second time it boots, afs finishes after a few minutes.  But
what does afs_cachetrim do?  I'm looking through the code, but since I
don't have a great familiarity with it, I can't quite tell... looks
like it's related to when the cache becomes too full, however this is
a completely empty cache I'm dealing with.


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