[OmniOS-discuss] Slow scrub on SSD-only pool

[Chris Siebenmann]

[About ZFS scrub tunables:]
> Interesting read - and it surely works. If you set the tunable before
> you start the scrub you can immediately see the thoughput being much
> higher than with the standard setting. [...]

 It's perhaps worth noting here that the scrub rate shown in 'zpool
status' is a cumulative one, ie the average scrub rate since the scrub
started. As far as I know the only way to get the current scrub rate is
run 'zpool status' twice with some time in between and then look at how
much progress the scrub's made during that time.

 As such, increasing the scrub speed in the middle of what had been a
slow scrub up to that point probably won't make a massive or immediate
difference in the reported scrub rate. You should see it rising over
time, especially if you drastically speeded it up, but it's not any sort
of instant jump.

(You can always monitor iostat, but that mixes in other pool IO. There's
probably something clever that can be done with DTrace.)

 This may already be obvious and well known to people, but I figured
I'd mention it just in case.

	- cks