[OpenIndiana-discuss] RAIDZ performance

[Edward Ned Harvey (openindiana)]

> From: Reginald Beardsley [mailto:pulaskite at yahoo.com]
> 
> 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.

In my experience, for sequential single threaded throughput, I consider each disk to be 1Gbit/sec, and they tend to add up exactly as you would wish.  That is to say, 
For a 3-disk raidz1, I expect 2Gbit
For a 4-disk raidz2, I expect 2Gbit

Your measurements do indeed seem to be significantly off.  I don't really have any suggestions why.