Michelle Sullivan
http://www.mhix.org/
Sent from my iPad

> On 09 May 2019, at 22:50, Alan Somers <asom...@freebsd.org> wrote:
> 
>> On Thu, May 9, 2019 at 5:37 AM Miroslav Lachman <000.f...@quip.cz> wrote:
>> 
>> Dimitry Andric wrote on 2019/05/09 13:02:
>>> On 9 May 2019, at 10:32, Miroslav Lachman <000.f...@quip.cz> wrote:
>> 
>> [...]
>> 
>>>> Disks are OK, monitored by smartmontools. There is nothing odd, just the 
>>>> long long scrubs. This machine was started with 4x 1TB (now 4x 4TB) and 
>>>> scrub was slow with 1TB disks too. This machine - HP ML110 G8) was my 
>>>> first machine with ZFS. If I remember it well it was FreeBSD 7.0, now 
>>>> running 11.2. Scrub was / is always about one week. (I tried some sysctl 
>>>> tuning without much gain)
>>> 
>>> Unfortunately https://svnweb.freebsd.org/changeset/base/339034, which
>>> greatly speeds up scrubs and resilvers, was not in 11.2 (since it was
>>> cut at r334458).
>>> 
>>> If you could update to a more recent snapshot, or try the upcoming 11.3
>>> prereleases, you will hopefully see much shorter scrub times.
>> 
>> Thank you. I will try 11-STABLE / 11.3-PRERELEASE soon and let you know
>> about the difference.
>> 
>> Kind regards
>> Miroslav Lachman
> 
> On 11.3 and even much older releases, you can greatly speed up scrub
> and resilver by tweaking some sysctls.  If you have spinning rust,
> raise vfs.zfs.top_maxinflight so they'll do fewer seeks.  I used to
> set it to 8192 on machines with 32GB of RAM.  Raising
> vfs.zfs.resilver_min_time_ms to 5000 helps a little, too.

I tried this, but I found that whilst it could speed up the resilver (and 
scrubs) by as much as 25% it also had a performance hit were reads 
(particularly streaming video - which is what my server mostly did) would 
“pause” and “stutter” .. the balance came when I brought it back to around 200 
* 15) .

It would still stutter when running multiple streams (to the point of heavy 
load) but that was kinda expected... I tried to keep the load distributed off 
it and let the other front end servers stream and it seemed to result in a 
healthy balance.

> 
> -Alan
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