Date: Sat, 06 Feb 2010 16:51:07 +0200 From: Urmas Lett <urmas.lett@eenet.ee> To: freebsd-fs@freebsd.org Subject: Re: Reading from ZFS mirror 2x slower than expected? Message-ID: <4B6D81DB.3090100@eenet.ee> In-Reply-To: <4B63088F.9030407@comcast.net> References: <4B619485.8080106@eenet.ee> <alpine.GSO.2.01.1001281350210.17824@freddy.simplesystems.org> <4B63088F.9030407@comcast.net>
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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@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@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@eenet.ee
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