On 02/20/2013 08:05 PM, Reginald Beardsley wrote: > On an N40L running oi_151a7 w/ four ST2000DM001 drives I'm seeing > a large drop in performance for RAIDZ2 vs RAIDZ1 which surprises me. > > The discussions google found were not entirely enlightening and not > OI based. How much CPU does a small OI based ZFS server need? > > For 3 disk RAIDZ1 I get 189-199 MB/s and 179 MB/s for 4 disk RAIDZ1. > But for 4 disk RAIDZ2 I get 109-118 MB/s. I expected some loss in > performance, but not that much. These are measured writing 64 GB > of /dev/zero to the RAIDZ filesystem from a console window. > > For a 256 GB file I got 111 MB/s writing and 279 MB/s reading 4 > disk RAIDZ2. > > System is unloaded w/ 4 GB of ECC DRAM using a 4-way mirror rpool > in the s0 slices w/ RAIDZ in the s1 slices. > > Does the drop in RAIDZ2 write performance correspond to other > people's experience? If so, why such a large hit? top suggests the > system has spare CPU capacity (30-50% idle). For my current needs > things look good, but I'd like to understand why a bit better. > Or if there is some tuning I should do.
RAID-Z2 is quite CPU intensive, since it switches from XOR parity (for RAID-Z1) to a Reed-Solomon error-correcting code (in order to be able to survive multiple drive failures). The N40L's piddly CPU (2 cores @ 1.4GHz) probably doesn't like that very much. 30-50% idle means 1 core completely saturated and the other running up to ~50% saturation. Try to switch to RAID-Z1 and watch as your CPU utilization drops dramatically - that's the source of your pain. Cheers, -- Saso _______________________________________________ OpenIndiana-discuss mailing list OpenIndiana-discuss@openindiana.org http://openindiana.org/mailman/listinfo/openindiana-discuss