ZFS Cheatsheet

Below is my cheatsheet for using ZFS.

Related Posts

• ZFS - Create Disk Pools - use this if you just want to set up your RAID array.
• Ubuntu 16.04 - Using Files To Test ZFS - learn ZFS by creating local files. No need to invest in buying disks first.
• Sharing ZFS Datasets Via NFS

Pools

List Pools

sudo zpool list  

Create a ZFS volume/pool on a single disk:

zpool create vol0 /dev/sd[x]  

Your pool will automatically be mounted at /[pool name].

Refer here for details of creating other pool types across multiple disks, such as RAID 1, 10, 5 etc.

Delete All Datasets In A Pool

zfs destroy -r [pool name] 

Delete a Pool

sudo zpool destroy [pool name]  

Check Disk Statuses

If you're running a redundant raid, you may want to check if any drives have failed once in a while. This is done by just checking the pools.

sudo zpool status  

Check Pool Balance

If you add to a pool that already contains data, your pool will initially be "unbalanced" and remain unbalanced until more data is written to the pool. This is because ZFS does not bother spreading the existing data around to make use of the new disks. If you keep adding data to the pool, it will eventually become balanced in terms of space utilized across the disks, but your existing data will still only be written on the initial disks unless you have it rewritten to the pool.

To check the balance of your pool, execute:

zpool list -v

Below is some example output of that command with my RAID10 pool that I recently added 2 x 8 TB drives to. As you can see, my array is heavily unbalanced and I will need to re-balance the array if I want to get much better performance.

NAME   SIZE  ALLOC   FREE  EXPANDSZ   FRAG    CAP  DEDUP  HEALTH  ALTROOT
zpool1  13.6T  4.21T  9.39T         -    15%    30%  1.00x  ONLINE  -
  mirror  3.62T  2.20T  1.43T         -    31%    60%
    sda      -      -      -         -      -      -
    sdb      -      -      -         -      -      -
  mirror  2.72T  1.65T  1.07T         -    32%    60%
    sdc      -      -      -         -      -      -
    sdd      -      -      -         -      -      -
  mirror  7.25T   368G  6.89T         -     2%     4%
    sde      -      -      -         -      -      -
    sdf      -      -      -         -      -      -

The easiest way to rebalance an array is probably to create a new temporary dataset, and move all the existing data to it, and then back again. By the end of the first move, the disks should be fairly utilized, but the individual files won't, and with the second pass, the files will also be fairly balanced. Beware of just using the mv command, because it will initially just copy the data until all of it has been written before deleting the original. You could easily run out of space. It would be better to use something like rsync as shown here to move the files one at a time.

Scrubbing

Scrub a pool

sudo zpool scrub [pool name]

To see the progress of a scrub use sudo zpool status

Datasets

Create a Dataset

sudo zfs create [pool name]/[dataset name]  

ZFS will automatically mount the dataset at /path/to/pool/[dataset name].

You can create a "descendent" dataset/filesystem like so:

sudo zfs create \  
[pool name]/[dataset name]/[descendent filesystem]

List Datasets and Pools

sudo zfs list  

Delete Dataset

sudo zfs destroy [pool name]/[dataset name]  

A dataset cannot be destroyed if snapshots or clones of the dataset exist.

Set Dataset Record Size

Read here for more information about what the record size actually does.

sudo zfs set recordsize=[size] pool/dataset/name

Size should be a value like 16k, 128k, or 1M etc.

Get Dataset Record Size

sudo zfs get recordsize pool/dataset/name

Snapshots

Snapshot Datasets

zfs snapshot [pool]/[dataset name]@[snapshot name]  

List Snapshots

sudo zfs list -t snapshot  

Rename Snapshots

zfs rename [pool]/[dataset]@[old name] [new name]  

Restore Snapshot

zfs rollback -r [pool]/[dataset]@[snapshot name]  

This will delete all snapshots that were taken after [snapshot name] was taken!

The file system that you want to roll back is unmounted and remounted, if it is currently mounted. If the file system cannot be unmounted, the rollback fails. The -f option forces the file system to be unmounted, if necessary.

Delete a Snapshot

zfs destroy tank/home/cindys@snap1  

Clones

@TODO

Creating RAID Arrays

Refer to my post on creating ZFS Pools.

Sharing Datasets Over NFS

Refer here.

Mounting

Mount Everything

zfs mount -a

This will let you know if your pool or dataset won't mount for some reason, such as the directory not being empty.

Get Mountpoints

zfs get all | grep mountpoint

Set Mountpoint

sudo zfs set mountpoint=/path/to/mount zpool-name/dataset-name

Mount A Specific Pool

sudo zfs mount $POOL_NAME

Deduplication

Enable Deduplication

sudo zfs set dedup=on zpool-name

Deduplication had a massive negative effect on performance for me on spinning disk.

Disable Deduplication

sudo zfs set dedup=off zpool-name

References

• Oracle Docs - Managing ZFS File Systems (Overview)
• Oracle - Sharing and Unsharing ZFS File Systems
• Ask Ubuntu - How do I mount a ZFS pool?
• Reddit - Anybody know how to check balance of vdevs in a pool?