How to speed up slow zpool scrub?

[krad]

thats a shame. I have used an ssd on usb before with success, as their
quality is usually better than pen drives.

On 26 April 2016 at 15:27, Miroslav Lachman <000.fbsd at quip.cz> wrote:

> krad wrote on 04/26/2016 16:02:
>
>> Erk, i would try to move your system off those data disks as you have
>> two pools competing for the disk spindles. This is never ideal. You can
>> by all means backup your os to those data pools but keep them on
>> separate physical mediums. A couple of small SSD would do the trick
>> nicely and could probably be added with no down time. You would probably
>> want to find a suitable window though to make sure the box reboots
>> nicely though.
>>
>
> The system pool is really small - only 15GB and scrub is done relatively
> fast. This machine cannot handle additional disks so I cannot move system
> to other devices anyway. I tried system on USB flashdisk (read only) in the
> past but it was slow and USB disk broke early.
>
> On 26 April 2016 at 14:35, Miroslav Lachman <000.fbsd at quip.cz
>> <mailto:000.fbsd at quip.cz>> wrote:
>>
>>     InterNetX - Juergen Gotteswinter wrote on 04/26/2016 15:09:
>>
>>         to speed up the scrub itself you can try
>>
>>         sysctl -w vfs.zfs.scrub_delay = 4 (default, 0 means higher prio)
>>
>>
>>     I will try it in the idle times
>>
>>         but be careful as this can cause a serious performance impact,
>>         the value
>>         can be changed on the fly
>>
>>         your pool is raidz, mirror ? dedup is hopefully disabled?
>>
>>
>>     I forgot to mention it. Disks are partitioned to four partitions:
>>
>>     # gpart show -l ada0
>>     =>        34  7814037101  ada0  GPT  (3.6T)
>>                34           6        - free -  (3.0K)
>>                40        1024     1  boot0  (512K)
>>              1064    10485760     2  swap0  (5.0G)
>>          10486824    31457280     3  disk0sys  (15G)
>>          41944104  7769948160     4  disk0tank0  (3.6T)
>>        7811892264     2144871        - free -  (1.0G)
>>
>>     diskXsys partitions are used for base system pool which is 4-way
>> mirror
>>
>>     diskXtank0 partitions are used for data storage as RAIDZ
>>
>>     # zpool list
>>     NAME    SIZE  ALLOC   FREE  EXPANDSZ   FRAG    CAP  DEDUP  HEALTH
>>     ALTROOT
>>     sys    14.9G  11.0G  3.92G         -    79%    73%  1.00x  ONLINE  -
>>     tank0  14.4T  10.8T  3.56T         -    19%    75%  1.00x  ONLINE  -
>>
>>
>>     # zpool status -v
>>        pool: sys
>>       state: ONLINE
>>        scan: scrub repaired 0 in 1h2m with 0 errors on Sun Apr 24
>>     04:03:54 2016
>>     config:
>>
>>              NAME              STATE     READ WRITE CKSUM
>>              sys               ONLINE       0     0     0
>>                mirror-0        ONLINE       0     0     0
>>                  gpt/disk0sys  ONLINE       0     0     0
>>                  gpt/disk1sys  ONLINE       0     0     0
>>                  gpt/disk2sys  ONLINE       0     0     0
>>                  gpt/disk3sys  ONLINE       0     0     0
>>
>>     errors: No known data errors
>>
>>        pool: tank0
>>       state: ONLINE
>>        scan: scrub in progress since Sun Apr 24 03:01:35 2016
>>              7.63T scanned out of 10.6T at 36.7M/s, 23h32m to go
>>              0 repaired, 71.98% done
>>     config:
>>
>>              NAME                STATE     READ WRITE CKSUM
>>              tank0               ONLINE       0     0     0
>>                raidz1-0          ONLINE       0     0     0
>>                  gpt/disk0tank0  ONLINE       0     0     0
>>                  gpt/disk1tank0  ONLINE       0     0     0
>>                  gpt/disk2tank0  ONLINE       0     0     0
>>                  gpt/disk3tank0  ONLINE       0     0     0
>>
>>     errors: No known data errors
>>
>>
>>     # zdb | grep ashift
>>                  ashift: 12
>>                  ashift: 12
>>
>>
>>     Thank you for your informations.
>>
>>
>>