On 14/02/2010 17:28, Jonathan Belson wrote:
After reading some earlier threads about zfs performance, I decided to test my
own server. I found the results rather surprising...
Thanks to everyone who responded. I experimented with my load.conf settings,
leaving me with the following:
vm.kmem_size="1280M"
vfs.zfs.prefetch_disable="1"
That kmem_size seems quite big for a machine with only (!) 2GB of RAM, but I
wanted to see if it gave better results than 1024MB (it did, an extra ~5MB/s).
The rest of the settings are defaults:
vm.kmem_size_scale: 3
vm.kmem_size_max: 329853485875
vm.kmem_size_min: 0
vm.kmem_size: 1342177280
vfs.zfs.arc_min: 104857600
vfs.zfs.arc_max: 838860800
My numbers are a lot better with these settings:
# dd if=/dev/zero of=/tank/test/zerofile.000 bs=1M count=2000
2000+0 records in
2000+0 records out
2097152000 bytes transferred in 63.372441 secs (33092492 bytes/sec)
# dd if=/dev/zero of=/tank/test/zerofile.000 bs=1M count=2000
2000+0 records in
2000+0 records out
2097152000 bytes transferred in 60.647568 secs (34579326 bytes/sec)
# dd if=/dev/zero of=/tank/test/zerofile.000 bs=1M count=2000
2000+0 records in
2000+0 records out
2097152000 bytes transferred in 68.241539 secs (30731312 bytes/sec)
# dd if=/dev/zero of=/tank/test/zerofile.000 bs=1M count=2000
2000+0 records in
2000+0 records out
2097152000 bytes transferred in 68.722902 secs (30516057 bytes/sec)
Writing a 200MB file to a UFS partition gives around 37MB/s, so the zfs overhead
is costing me a few MB per second. I'm guessing that the hard drives themselves
have rather sucky performance (I used to use Spinpoints, but receiving three
faulty ones in a row put me off them).
Reading from a raw device:
# dd if=/dev/ad4s1a of=/dev/null bs=1M count=2000
1024+0 records in
1024+0 records out
1073741824 bytes transferred in 11.286550 secs (95134635 bytes/sec)
# dd if=/dev/ad4s1a of=/dev/null bs=1M count=2000
1024+0 records in
1024+0 records out
1073741824 bytes transferred in 11.445131 secs (93816473 bytes/sec)
# dd if=/dev/ad4s1a of=/dev/null bs=1M count=2000
1024+0 records in
1024+0 records out
1073741824 bytes transferred in 11.284961 secs (95148032 bytes/sec)
Reading from zfs file:
# dd if=/tank/test/zerofile.000 of=/dev/null bs=1M count=4000
2000+0 records in
2000+0 records out
2097152000 bytes transferred in 25.643737 secs (81780281 bytes/sec)
# dd if=/tank/test/zerofile.000 of=/dev/null bs=1M count=4000
2000+0 records in
2000+0 records out
2097152000 bytes transferred in 25.444214 secs (82421567 bytes/sec)
# dd if=/tank/test/zerofile.000 of=/dev/null bs=1M count=4000
2000+0 records in
2000+0 records out
2097152000 bytes transferred in 25.572888 secs (82006851 bytes/sec)
So, the value of arc_max from the zfs tuning wiki seemed to be the main brake on
performance.
Cheers,
--Jon
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