Areca vs. ZFS performance testing.

[Danny Carroll]

I'd like to post some results of what I have found with my tests.
I did a few different types of tests.  Basically a set of 5-disk tests
and a set of 12-disk tests.

I did this because I only had 5 ports available on my onboard controller
and I wanted to see how the areca compared to that.  I also wanted to
see comparisons between JBOD, Passthru and hardware raid5.

I have not tested raid6 or raidz2.

You can see the results here:
http://www.dannysplace.net/quickweb/filesystem%20tests.htm

An explanation of each of the tests:
ICH9_ZFS			5 disk zfs raidz test with onboard SATA
				ports.
ARECAJBOD_ZFS			5 disk zfs raidz test with Areca SATA
				ports configured in JBOD mode.
ARECAJBOD_ZFS_NoWriteCache	5 disk zfs raidz test with Areca SATA 					
ports configured in JBOD mode and with
				disk caches disabled.
ARECARAID			5 disk zfs single-disk test with Areca
				raid5 array.
ARECAPASSTHRU			5 disk zfs raidz test with Areca SATA 						ports
configured in Passthru mode.  This
				means that the onboard areca cache is
				active.
ARECARAID-UFS2			5 disk ufs2 single-disk test with Areca
				raid5 array.
ARECARAID-BIG			12 disk zfs single-disk test with Areca
				raid5 array.
ARECAPASSTHRU_12		12 disk zfs raidz test with Areca SATA 						ports
configured in Passthru mode.  This
				means that the onboard areca cache is
				active.


I'll probably be opting for the ARECAPASSTHRU_12 configuration.   Mainly
because I do not need amazing read speeds (network port would be
saturated anyway) and I think that the raidz implementation would be
more fault tolerant.  By that I mean if you have a disk read error
during a rebuild then as I understand it, raidz will write off that
block (and hopefully tell me about dead files) but continue with the
rest of the rebuild.

This is something I'd love to test for real, just to see what happens.
But I am not sure how I could do that.  Perhaps removing one drive, then
 a few random writes to a remaining disk (or two) and seeing how it goes
with a rebuild.

Something else worth mentioning.   When I converted from JBOD to
passthrough, I was able to re-import the disks without any problems.
This must mean that the areca passthrough option does not alter the disk
much, perhaps not at all.

After a 21 hour rebuild I have to say I am not that keen to do more of
these tests, but if there is something someone wants to see, then I'll
definitely consider it.

One thing I am at a loss to understand is why turning off the disk
caches when testing the JBOD performance produced almost identical (very
slightly better) results.  Perhaps it was a case of the ZFS internal
cache making the disks cache redundant?  Comparing to the ARECA
passthrough (where the areca cache is used) shows again, similar results.

-D