zpool

From zfs-101: “A zpool contains one or more vdevs, each of which in turn contains one or more devices.”

Create

To setup a RAIDz2 pool use zpool create:

zpool create NAME -o ashift=12 raidz2 \
    /dev/disk/by-id/DISK1 /dev/disk/by-id/DISK2 /dev/disk/by-id/DISK3 \
    /dev/disk/by-id/DISK4 /dev/disk/by-id/DISK5

Alternatively, create a mirror pool tank:

sudo zpool create -m /mnt/tank tank mirror sdc1 sdd1

To change the mount point:

sudo zfs set mountpoint=/mnt/btr btr

Status Monitoring / Clear

Use zpool status:

To look at the pool status:

zpool status

To monitor it in real time:

zpool status -v 5

or use zpool iostat:

zpool iostat -v 5

For example:

root@nass[~]# zpool status tank
  pool: tank
 state: ONLINE
status: One or more devices has experienced an unrecoverable error.  An
	attempt was made to correct the error.  Applications are unaffected.
action: Determine if the device needs to be replaced, and clear the errors
	using 'zpool clear' or replace the device with 'zpool replace'.
   see: https://openzfs.github.io/openzfs-docs/msg/ZFS-8000-9P
  scan: scrub repaired 0B in 07:12:57 with 0 errors on Tue Jan 17 18:12:00 2023
config:

	NAME        STATE     READ WRITE CKSUM
	tank        ONLINE       0     0     0
	  raidz2-0  ONLINE       0     0     0
	    sde     ONLINE       0     0     0
	    sdd     ONLINE       0     0     0
	    sdc     ONLINE       0     0     0
	    sdb     ONLINE       0     0     0
	    sda     ONLINE       0     1     0

errors: No known data errors

Note write errors is non-zero. From the doc:

The READ and WRITE columns provide a count of I/O errors that occurred on the device, while the CKSUM column provides a count of uncorrectable checksum errors that occurred on the device. Both error counts indicate a potential device failure, and some corrective action is needed. If non-zero errors are reported for a top-level virtual device, portions of your data might have become inaccessible.

I decided to clear the status, for now, because smartctl for sda does not report any problems. sda is the oldest drive in the above pool, so I plan to keep an eye on it.

Use zpool clear:

root@nass[~]# zpool clear tank
root@nass[~]# zpool status tank
  pool: tank
 state: ONLINE
  scan: scrub repaired 0B in 07:12:57 with 0 errors on Tue Jan 17 18:12:00 2023
config:

	NAME        STATE     READ WRITE CKSUM
	tank        ONLINE       0     0     0
	  raidz2-0  ONLINE       0     0     0
	    sde     ONLINE       0     0     0
	    sdd     ONLINE       0     0     0
	    sdc     ONLINE       0     0     0
	    sdb     ONLINE       0     0     0
	    sda     ONLINE       0     0     0

errors: No known data errors

Good read: Failure Trends in a Large Disk Drive Population

Upgrade

Use zpool upgrade:

$ zpool --version
    zfs-0.8.3-1ubuntu12.14
    zfs-kmod-0.8.3-1ubuntu12.14
$ sudo zpool upgrade -a

Scrubbing

Use zpool scrub:

sudo zpool scrub pool0