Scrubbing practices?

[steamace1]

Well on a freenas 8.3.1 that has been working well for about a month, today I started my first scrub today on a raid-z volume. Soon after the web-gui stopped responding and it appeared to restart so my questions are:

-Is it normal for the server to restart when starting a scrub?
-Does it ever try to scrub in an offline state? example, power down and before the gui loads continue or resume a scrub?

 

[cyberjock]

A scrub shouldn't affect the web-gui normally. The worse case scenario is there will be heavy latency due to high CPU usage during a scrub.

A server shouldn't restart when starting a scrub.
During startup when the zpools are mounted a scrub will auto-resume. Depending on how powerful your system your startup time can be extended by a few seconds to a few minutes because the scrub will resume while you are still booting up and both will compete for CPU resources.

Also, depending on your zpool you may have slower access to the file shares while the scrub is performed. For this reason scrubs should be scheduled during off-hours on the server.

 

[steamace1]

A scrub shouldn't affect the web-gui normally. The worse case scenario is there will be heavy latency due to high CPU usage during a scrub.

A server shouldn't restart when starting a scrub.
During startup when the zpools are mounted a scrub will auto-resume. Depending on how powerful your system your startup time can be extended by a few seconds to a few minutes because the scrub will resume while you are still booting up and both will compete for CPU resources.

Also, depending on your zpool you may have slower access to the file shares while the scrub is performed. For this reason scrubs should be scheduled during off-hours on the server.

another question comes to mind, what would happen if you scrubbed a pool that was already being scrubbed?

Edit:
Also is a scrub rate of 458 MB/s a good average for 3 drives? I was thinking it should be around 600.

 

[cyberjock]

There are a whole list of factors that affect scrubs.I'd say 458MB/sec is really good for 3 drives. 600MB/sec is physically impossible unless you are using SSDs...

You can't start a scrub on a zpool that is already scrubbing.. try it.. you'll get an error. :P

 

[AVB]

There are a whole list of factors that affect scrubs.I'd say 458MB/sec is really good for 3 drives. 600MB/sec is physically impossible unless you are using SSDs...

I don't know if you mean for 3 drives or that 600M/s is impossible in general but I am doing a scrub right now and getting 671M/s from 6 Seagate 3TB 7200RPM drives (Raid Z1) with 10.2TB on them.

 

[cyberjock]

600M/s from 3 disks means that each disk would have to have 200MB/sec each. For an SSD that's achievable. That's really really high for platter based media. My drives do just barely over 100MB/sec, so if I had 3 disks I'd be at their limit to get 300MB/sec. That's also assuming purely sequential reads with no disk head movement.

6 disks at 671MB/sec is just over 100MB/sec per disk, which is very realistic.