[StavrosK]

I have a home server with three disks and ZFS, for my photos and things, so I'm not an expert. However, Ubuntu's md-raid includes scrubbing once a week by default, and I added scrubbing to my ZFS setup via crontab, again once a week (I'm not sure if ZFS does it automatically, but I don't think it does. I would appreciate a correction, if someone knows for sure).

The article assumes no scrubbing, which is a stupid thing to run without, as detailed from the article. So it's basically "why pointing a gun at your foot and pulling the trigger is bad", "because you're going to shoot yourself in the foot".

[jrockway]

The article describes why scrubs don't happen often enough: it's slow and disruptive. I have a 3-way RAID-1 /home partition (long story) and it's checked on the first Sunday of the month. I always remember this because I can tell from the performance of my workstation that something is up with the disk. This is with operations like a single thread running "ls". If you're running a production service, you're also going to notice, and you're also going to have more than 3TB of drive to scan. That makes running regular scans rather difficult.

[olgeni]

You may add something like this to /etc/periodic.conf:

daily_status_zfs_enable="YES" daily_scrub_zfs_enable="YES" daily_scrub_zfs_default_threshold="6" # in days

and it will scrub the pools every 6 days (and send you a report in the daily run output).

[StavrosK]

Very nice, thank you, I will try that. I am rather dismayed, however, by learning in this thread that my disks have 4K sector sizes and ZFS autodetected 512 bytes, which means I'll have to destroy the pool and recreate it...

[olgeni]

It happens all the time...

If you run "camcontrol identify ada0" (or whatever your device is) you can find out before it is too late:

sector size logical 512, physical 512, offset 0

This is from a lucky drive of course :)

[StavrosK]

Hmm, there's no such command in Ubuntu, maybe it's from BSD?

[olgeni]

camcontrol is from FreeBSD.

I don't have a Linux box available right now but maybe "hdparm -I" does something similar: "request identification info directly from the drive".

[StavrosK]

Yep, that works:

    Logical  Sector size:                   512 bytes
    Physical Sector size:                  4096 bytes

I'm guessing that's not very nice. My ZFS pool was created with ashift 9 (this is 2^9=512 bytes), when it should be 12 (2^12=4096). I will have to copy everything off and back on again.

For everyone who wants to check, and because I couldn't find info on it, run:

    zdb | grep ashift

And see if it's 9 or 12.

[X-Istence]

ZFS doesn't do it automatically, you have to crontab it. I have it crontabbed for the 1st or the 15th.