ZFS...

[Michelle Sullivan]

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

> On 09 May 2019, at 22:50, Alan Somers <asomers at freebsd.org> wrote:
> 
>> On Thu, May 9, 2019 at 5:37 AM Miroslav Lachman <000.fbsd at quip.cz> wrote:
>> 
>> Dimitry Andric wrote on 2019/05/09 13:02:
>>> On 9 May 2019, at 10:32, Miroslav Lachman <000.fbsd at 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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