zfs benchmarks and 7 disk raidz oddity
Andrew Snow
andrew at modulus.org
Sat Sep 20 09:31:17 UTC 2008
Hi all,
I am running 8-CURRENT with ZFS patches on a 3ghz Core2Duo with Intel
P45 chipset. I took some benchmarks of ZFS on six old SATA disks and
one PATA, onboard controllers only, and I expect you are interested to
see the results. The disks range in size from 200gb to 320gb.
I tried several configurations with quick and dirty testing. Listed
below is the sequential megabytes/sec rating as measured by dd bs=1m for
a 10GB file. All ZFS settings were left at their defaults.
Conf Write Read (MB/s)
------------------------------------
7 disk RAIDZ2 220 305
7 disk RAIDZ1 84 361
7 disk striped 318 409
7 disk stripe copies=2 140 164
6 disk RAIDZ2 173 260
6 disk RAIDZ1 238 307
6 disk striped 280 346
6 disk 2xRAIDZ1 striped 188 251
6 disk striped mirrors 164 323
6 disk stripe copies=2 151 179
A few notes:
1. using copies=2 is a nice way to be able to get RAID1-like mirroring
reliability but on an odd number of disks. However you take a
noticeable performance penalty: Write speed is fine but read speed is
almost half of what RAID0+1 achieved.
2. RAIDZ1 and RAIDZ2 are fast and efficient. However in total it caused
the system to use almost all of one CPU core during writing.
3. There seemed to be a bug with 7 disks and RAIDZ1 - the write
performance was terrible! When I ran "gstat" I noticed it was spending
much time writing to only two disks most of the time, which became a
serious bottleneck - the worst write score of the lot. Read was fine.
Perhaps the algorithm isn't optimised for choosing parity locations out
of exactly 7 disks?
- Andrew
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