xattr performance and Samba4

[tridge at samba.org]

Those of you who have been following the Samba4 svn commit messages
will know that we've been making quite a lot of progress on the posix
NTVFS backend. It can now do alternate data streams, 4 timestamps,
store/fetch of NT ACLs and a few other new tricks.

All of this means that many of the new features in Samba4 will be
heavily reliant on the filesystem supporting user xattrs. To see how
much this will cost us in performance I've been doing some
benchmarking on Linux with a new version of dbench that is designed to
simulate the filesystem access patterns of Samba4 under a NetBench
load, both with and without xattrs.

The results are quite interesting, and show quite a large difference
between the different Linux filesystems. I haven't tested any
non-Linux systems that support xattrs yet.

See http://samba.org/~tridge/xattr_results/ for pretty graphs, and
some description of the tests along with the test scripts used.

Cheers, Tridge