Speeding up resilvering

[Matthew Seaman]

On 07/08/15 15:28, Mike Tancsa wrote:
>> Look at the IO saturation on the disk channel(s) involved with either
>> > systat -vm or iostat.  If the channel is saturated then there's nothing
>> > you can do in terms of tuning; the question then turns to why actual I/O
>> > performance is so poor and has to be addressed there.

> I had one server that was taking ages, and it turned out to be the
> controller, not the disk that was hosed. As Karl suggested, take a look
> at the throughput on gstat. Is anyone disk or groups of disks lagging
> far behind on write speeds ?  In my case, it was a very obvious and
> glaring outlier.

Thanks for the suggestions.  I've been playing with gstat et al, and as
far as I can tell, all the drives are behaving reasonably well.  I'm
certainly getting 90-100% capacity (mostly reads) continually on the
original drives whilst the new one (mostly writes) seems to go in
bursts.  Which is pretty much what I'd expect when resilvering a RAIDZ.

So, having exhausted that, I actually sat down and timed what progress
it was making rather more carefully.  Turns out my impression that
applying the sysctl tweaks I mentioned previously had little effect was
wrong.  Current projection is about 50h total to do the resilvering,
which is much, much better than the approx 12days I was expecting
previously.  In fact, that's pretty much inline with what I'd expect
from this hardware.

	Cheers,

	Matthew



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