[OpenIndiana-discuss] RAIDZ performance

[Reginald Beardsley]

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. 

Have Fun!
Reg