Re: btrfs balance problems

[James Courtier-Dutton <james.dutton@gmail.com>]

On 28 December 2017 at 00:39, Duncan <1i5t5.duncan@cox.net> wrote:
>
> AFAIK, ionice only works for some IO schedulers, not all.  It does work
> with the default CFQ scheduler, but I don't /believe/ it works with
> deadline, certainly not with noop, and I'd /guess/ it doesn't work with
> block-multiqueue (and thus not with bfq or kyber) at all, tho it's
> possible it does in the latest kernels, since multi-queue is targeted to
> eventually replace, at least as default, the older single-queue options.
>
> So which scheduler are you using and are you on multi-queue or not?
>

Thank you. The install had defaulted to deadline.
I have now switched it to CFQ, and the system is much more
responsive/interactive now during a btrfs balance.

I will test it when I next get a chance, to see if that has helped me.
After reading about it:
deadline:  more likely to complete long sequential reads/writes and
not switch tasks.Thus reducing the amount of seeking but impacting
concurrent tasks.
cfq: more likely to break up long sequential reads/writes to permit
other tasks to do some work. Thus increasing the amount of seeking but
helping concurrent tasks.

This would explain why "cfq" is best for me.
I have not yet looked at "multi-queue".