Re: RAID10 Balancing Request for Comments and Advices

[Vincent Olivier <vincent@up4.com>]

> On Jun 16, 2015, at 8:14 PM, Chris Murphy <lists@colorremedies.com> wrote:
> 
> On Tue, Jun 16, 2015 at 5:58 PM, Duncan <1i5t5.duncan@cox.net> wrote:
> 
>> On a current kernel unlike older ones, btrfs actually automates entirely
>> empty chunk reclaim, so this problem doesn't occur anything close to near
>> as often as it used to.  However, it's still possible to have mostly but
>> not entirely empty chunks that btrfs won't automatically reclaim.  A
>> balance can be used to rewrite and combine these mostly empty chunks,
>> reclaiming the space saved.  This is what Hugo was recommending.
> 
> Yes, as little as a -dusage=5 (data chunks that are 5% or less full)
> can clear the problem and is very fast, seconds. Possibly a bit
> longer, many seconds o single digit minutes is -dusage=15. I haven't
> done a full balance in forever.


Yes, on this 80% full 6x4TB RAID10 -dusage=15 took 2 seconds and relocated "0 out of 3026 chunks”.

Out of curiosity, I had to use -dusage=90 to have it relocate only 1 chunk and it took les than 30 seconds.

So I put a -dusage=25 in the weekly cron just before the scrub.

FYI.

Thanks for your help.