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From Ben Smith-Mannschott <bsmith.o...@gmail.com>
Subject an observation regarding FSFS performance on BTRFS
Date Mon, 12 Sep 2011 13:44:20 GMT
I've made the observation that FSFS repositories perform better on
EXT4 than BTRFS. This probably isn't ground-breaking, but I thought
I'd share it.

I've got two Linux machines:

- colossus, using BTRFS spanned over two disks.
  2.6.38-11-generic #48-Ubuntu SMP Fri Jul 29 19:02:55 UTC 2011
  x86_64 x86_64 x86_64 GNU/Linux

- oberon, using EXT4 on a 2-disk software RAID-1 set.
  Linux oberon 2.6.32-33-generic #72-Ubuntu SMP Fri Jul 29 21:07:13 UTC 2011
  x86_64 GNU/Linux

I've noticed that writes to FSFS repositories are 5x faster under EXT4
than BTRFS. When svnsyncing form the same svn:// source to an local
repository (file://), oberon completes about 400 revisions in the time
it takes colossus to grind through 80.

The BTRFS machine is our build server. Performance with (1.6.x)
working copies is quite acceptable, but I'm glad I'm not using it to
host svn repositories.

Looks like the BTRFS people have some work to do. Maybe current
Kernels have already improved this picture. I know there has been
recent work on reducing the cost of meta-data operations (e.g. file
creation, ...) and that work is ongoing on defragmentation
functionality because of poor performance on files that are modified
in place heavily (e.g. sqlite).

// ben

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