Date: Sat, 20 Sep 2008 19:30:18 +1000 From: Andrew Snow <andrew@modulus.org> To: freebsd-fs@freebsd.org Subject: zfs benchmarks and 7 disk raidz oddity Message-ID: <48D4C2AA.8080000@modulus.org>
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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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