ZFS commands cheatsheet

Devices and Pools

List all devices in the server

lsblk -S

List all pools

zpool list

Clear device errors from a pool and try to rebuild the pool

zpool clear

Create a zpool called 'files' in RAID 0 using /dev/sd[b,c,d]

zpool create -f files /dev/sdb /dev/sdc /dev/sdd

Optional Parameters -m mountpoint Sets the mount point for the root dataset. The default mount point is /pool or altroot/pool if altroot is specified. The mount point must be an absolute path, legacy, or none. For more information on dataset mount points, see zfs(8).

Create a zpool called 'files' in RAID 1 (Mirrored) using /dev/sda and /dev/sdb

zpool create files mirror /dev/sda /dev/sdb used striped instead of mirror for RAID 5

Change the base mountpoint of an existing ZFS Pool called $POOL to $NEWPATH

zfs set mountpoint=$NEWPATH $POOL

Kill a pool named $POOL

zpool destroy $POOL

File Systems

ZFS file systems live 'inside' pools. By default they are mounted under the parent pool.

For example:

>zfs get mountpoint big
NAME  PROPERTY    VALUE                      SOURCE
big   mountpoint  /var/lib/snapd/hostfs/big  local

>zfs create big/docker   # docker is a filesystem in the pool named big

>zfs get mountpoint big/docker
NAME        PROPERTY    VALUE                             SOURCE
big/docker  mountpoint  /var/lib/snapd/hostfs/big/docker  inherited from big

As you can see, big is mounted in /var/lib/snapd/hostfs/big and big/docker is mounted in /var/lib/snapd/hostfs/big/docker and it's that inherited from /big.

But what if we want big/docker to be mounted in /var/lib/docker?

>zfs set mountpoint=/var/lib/docker big/docker

>zfs get mountpoint big/docker
NAME        PROPERTY    VALUE            SOURCE
big/docker  mountpoint  /var/lib/docker  local

List file systems

zfs list shows all file systems
zfs list -r small shows all file systems under small
zfs list -t snapshot shows all snapshots

Snapshots

Snapshots capture a point in time of a file system. Snapshots can't be accessed directly, but you can clone them, back them up, and roll back to them.

Create a snapshot

To create a filesystem snapshot, we use the zfs snapshot command.

We have a filesystem called test, mounted in my home directory.

zfs list -r big/test
NAME       USED  AVAIL  REFER  MOUNTPOINT
big/test    96K  4.36T    96K  /home/mrunkel/test

I create a snapshot of the filesystem.

> zfs snapshot big/test@demo
> zfs list -t snapshot
NAME                                                                                           USED  AVAIL  REFER  MOUNTPOINT
big/test@demo                                                                                    0B      -    96K  -

Rollback a snapshot

Now let's create a file in there.

> touch /home/mrunkel/test/afile.txt
> ls /home/mrunkel/test/
afile.txt

Now let's rollback to the snapshot.

> zfs rollback big/test@demo
> ls /home/mrunkel/test/
<nothing is shown>

Clone a snapshot

You can make a copy of a snapshot into a new filesystem..

Here we take the snapshot we created above big/test@demo and create a new zfs filesystem big/demobackup from it.

> zfs clone big/test@demo big/demobackup

Note: Snapshots that are used to create cloned file systems can't be deleted until the file system is deleted.

Clone a snapshot to another machine!

You can also 'send' your snapshot to another machine..

Here we're sending the big/test@demo snapshot to othermachine into the backup/test filesystem.

zfs send big/test@demo | ssh othermachine zfs recv backup/test

Obviously, the other machine will also need to have ZFS installed

mrunkel/zfs_cheatsheet.md