How to speed up slow zpool scrub?

[DH]

>5GB of RAM 

That seems to be an insufficient amount of system ram when employing zfs.

Take a look at this:

http://doc.freenas.org/9.3/freenas_intro.html#ram


David Hutchens III 
System Administrator

--------------------------------------------
On Tue, 4/26/16, Miroslav Lachman <000.fbsd at quip.cz> wrote:

 Subject: How to speed up slow zpool scrub?
 To: freebsd-fs at freebsd.org
 Date: Tuesday, April 26, 2016, 5:44 AM
 
 Hi,
 
 is there any way to make zpool scrub faster?
 We have one older machine with CPU Pentium(R) Dual E2160
 @1.80GHz, 5GB 
 of RAM and 4x 4TB HDDs. It is just a storage for backups for
 about 20 
 machines.
 Scrub is scheduled from periodic each 30 days but it takes
 about 4 days 
 to complete and everything during scrub is slow. Backups
 takes 8 hours 
 instead of 5 (made by rsync), deleting of old files is even
 more slower.
 
 The backups are made every night from the midnight to
 morning, the 
 machine is idle for the rest of the day.
 
 Is there any tuning to make scrub faster in this idle time?
 Or is it better to do it other way - slower scrub with even
 lower 
 priority taking for about one week but not affecting time of
 normal 
 operations? (is it dangerous to have scrub running this long
 or reboot 
 machine during the scrub?)
 
 I have a performance graphs of this machine and CPU is about
 70% idle 
 during scrub, but hard drives are busy 75% (according to
 iostat)
 
 FreeBSD 10.3-RELEASE amd64 GENERIC
 
 Miroslav Lachman
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