Re: Benchmark (Phoronix): FreeBSD 9.0-RC2 vs. Oracle Linux 6.1 Server

Am 15.12.2011 11:10, schrieb Michael Larabel:
> No, the same hardware was used for each OS.
> 
> In terms of the software, the stock software stack for each OS was used.

Just curious: Why did you choose ZFS on FreeBSD, while UFS2 (with
journaling enabled) should be an obvious choice since it is more similar
in concept to ext4 and since that is what most FreeBSD users will use
with FreeBSD?

Did you tune the ZFS ARC (e.g. vfs.zfs.arc_max="6G") for the tests?

And BTW: Did your measured run times account for the effect, that Linux
keeps much more dirty data in the buffer cache (FreeBSD has a low limit
on dirty buffers since under realistic load the already cached data is
much more likely to be reused and thus more valuable than freshly
written data; aggressively caching dirty data would significantly reduce
throughput and responsiveness under high load). Given the hardware specs
of the test system, I guess that Linux accepts at least 100 times the
dirty data in the buffer cache, compared to FreeBSD (where this number
is at most in the tens of megabyte range).

If you did not, then your results do not represent a server load (which
I'd expect relevant, if you are testing against Oracle Linux 6.1
server), where continuous performance is required. Tests that run on an
idle system starting in a clean state and ignoring background flushing
of the buffer cache after the timed program has stopped are perhaps
useful for a very lowly loaded PC, but not for a system with high load
average as the default.

I bet that if you compared the systems under higher load (which
admittedly makes it much harder to get sensible numbers for the program
under test) or with reduced buffer cache size (or raise the dirty buffer
limit in FreeBSD accordingly, which ought to be possible with sysctl
and/or boot time tuneables, e.g. "vfs.hidirtybuffers").

And a last remark: Single benchmark runs do not provide reliable data.
FreeBSD comes with "ministat" to check the significance of benchmark
results. Each test should be repeated at least 5 times for meaningful
averages with acceptable confidence level.

Regards, STefan