Reading from ZFS mirror 2x slower than expected?
Urmas Lett
urmas.lett at eenet.ee
Sat Feb 6 14:51:16 UTC 2010
Steve Polyack wrote:
> I can also vouch that the mirror performance is less than stellar.
> Writes are also about 50% slower than single-disk performance, although
> this may be expected due to checksums / other ZFS overhead. I can try
> to provide more details when I get time.
I'm luckily observing only 50% slowness when reading from mirror.
Writing seems to be OK.
dd if=/dev/zero of=test.bin bs=1m count=8192
8589934592 bytes transferred in 143.145040 secs (60008608 bytes/sec)
systat -vm shows 400+ tps per disk
dd if=test.bin of=/dev/null bs=1m
8589934592 bytes transferred in 155.068721 secs (55394373 bytes/sec)
Disks ada0 ada1 ada2 pass0 pass1 pass2
KB/t 0.00 128 128 0.00 0.00 0.00
tps 0 226 224 0 0 0
MB/s 0.00 28.30 28.06 0.00 0.00 0.00
%busy 0 54 64 0 0 0
systat -vm shows only 200+ tps per disk
After detaching one disk from mirror:
dd if=test.bin of=/dev/null bs=1m
8589934592 bytes transferred in 149.991512 secs (57269471 bytes/sec)
Disks ada0 ada1 ada2 pass0 pass1 pass2
KB/t 0.00 128 0.00 0.00 0.00 0.00
tps 0 444 0 0 0 0
MB/s 0.00 55.55 0.00 0.00 0.00 0.00
%busy 0 98 0 0 0 0
systat -vm shows 400+ tps
Now I did simple test on the same hardware with Belenix 7.1 liveCD:
jack at belenix:/zpool0# dd if=/dev/zero of=8gb.test bs=1024k count=8192
8192+0 records in
8192+0 records out
8589934592 bytes (8.6 GB) copied, 167.512 s, 51.3 MB/s
jack at belenix:/zpool0# dd if=8gb.test of=/dev/null bs=1024k
8192+0 records in
8192+0 records out
8589934592 bytes (8.6 GB) copied, 82.4957 s, 104 MB/s
read speed from mirror is 2x better and Solaris iostat shows 400+ tps
and 50+ MB/s per mirrored disk.
--
Urmas Lett
Tel: +(372) 7 302 110
Fax: +(372) 7 302 111
E-Mail: urmas.lett at eenet.ee
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