Published: January 23, 2022

Getting Started with ZFS

These are my notes from setting up a ZFS file server on FreeBSD.

For this project, I will be configuring four drives in an external Thunderbolt 2 enclosure from OWC that connects to my 2013 Mac Pro.

My plan is to create a mirrored zpool with two 500GB SSDs and have a single-disk zpool for my 2TB drive. I have another 128GB SSD in the enclosure that will be formatted as UFS for “scratch” data.

Initializing Drives

I like the idea of setting each disk’s serial number as the drive label because it is an unambiguous reference. Importantly, the serial number is nearly always accessible. It’s both printed on the physical drive and available via disk utility programs. When you need to replace a drive, it’s really helpful to know exactly what drive to touch. (Or type!)

With that in mind, the first thing we want to do is find where our drives are currently located in the machine:

$ camcontrol devlist
<SHGS31-500GS-2 90000Q00>          at scbus0 target 0 lun 0 (pass0,ada0)
<SHGS31-500GS-2 90000Q00>          at scbus1 target 0 lun 0 (pass1,ada1)
<M4-CT128M4SSD2 0309>              at scbus2 target 0 lun 0 (pass2,ada2)
<WDC WD20SPZX-08UA7 02.01A02>      at scbus3 target 0 lun 0 (pass3,ada3)
<APPLE SSD SM0256G BXW8SA0Q>       at scbus4 target 0 lun 0 (pass4,ada4)

Now, we have a few ways of getting the serial number, but if you decide to grab it from software, please also make sure the same value is printed on the actual physical drive label.

We could use camcontrol identify or geom disk list, but in this case we can grep over dmesg in a clever way to grab all our drive serial numbers at once.

$ dmesg | grep -B1 'Serial Number'
ada0: <SHGS31-500GS-2 90000Q00> ACS-3 ATA SATA 3.x device
ada0: Serial Number ESA8N416111408609
ada1: <SHGS31-500GS-2 90000Q00> ACS-3 ATA SATA 3.x device
ada1: Serial Number ESA8N41611140860U
ada2: <M4-CT128M4SSD2 0309> ACS-2 ATA SATA 3.x device
ada2: Serial Number 0000000012020907C404
ada3: <WDC WD20SPZX-08UA7 02.01A02> ACS-3 ATA SATA 3.x device
ada3: Serial Number WD-WXP2E31CV0WZ
ada4: <APPLE SSD SM0256G BXW8SA0Q> ATA8-ACS SATA 3.x device
ada4: Serial Number S216NYAH100559

Now let’s initialize the drives.1 ZFS will enable TRIM by default for drives that support it.

WARNING! You could destroy your system if you type the wrong drive number here!

$ gpart create -s gpt ada0
ada0 created

$ gpart add -t freebsd-zfs -l ESA8N416111408609 -a 1M ada0
ada0p1 added

$ gpart create -s gpt ada1
ada1 created

$ gpart add -t freebsd-zfs -l ESA8N41611140860U -a 1M ada1
ada1p1 added

$ gpart create -s gpt ada3
ada3 created

$ gpart add -t freebsd-zfs -l WD-WXP2E31CV0WZ -a 1M ada3
ada3p1 added

After creating all of your new partitions you can check out the results with gpart show -lp. After setting the GPT drive labels the partitions can be referenced by /dev/gpt/$SERIAL_NUMBER.

Configuring ZFS

I’m hoping the FreeBSD handbook’s entry on ZFS will be enough to get everything setup.

The first thing it wants us to do is enable ZFS on the system.

$ echo 'zfs_enable="YES' >> /etc/rc.conf
$ service zfs start

Single drive (backup)

Even for a single drive, the first step is to create our zpool:

$ zpool create backup /dev/gpt/WD-WXP2E31CV0WZ

If you get the error: must be a block device or regular file, make sure you are running zpool create as root.

We can see that it worked by checking the output of df, zpool status, or zpool list.

$ df
Filesystem         Size    Used   Avail Capacity  Mounted on
/dev/gpt/rootfs     77G    5.1G     66G     7%    /
devfs              1.0K    1.0K      0B   100%    /dev
backup             1.8T     96K    1.8T     0%    /backup
$ zpool status
  pool: backup
 state: ONLINE

        NAME                   STATE     READ WRITE CKSUM
        backup                 ONLINE       0     0     0
          gpt/WD-WXP2E31CV0WZ  ONLINE       0     0     0

errors: No known data errors
$ zpool list
backup  1.81T   360K  1.81T        -         -     0%     0%  1.00x    ONLINE  -

Now we can create the filesystem, also known as a dataset. I think adding compression and turning off access time are enough customization’s for now.

$ zfs create -v -o atime=off -o compression=on backup/data
create backup/backup-data

Mirrored drives (data)

The first step is to create a mirrored zpool:

$ zpool create storage mirror /dev/gpt/ESA8N416111408609 /dev/gpt/ESA8N41611140860U

Now, create the dataset.

$ zfs create -v -o atime=off -o compression=on storage/data
create storage/storage-data

Looks good!

$ df -h
Filesystem              Size    Used   Avail Capacity  Mounted on
/dev/gpt/rootfs          77G    5.1G     66G     7%    /
devfs                   1.0K    1.0K      0B   100%    /dev
backup                  1.8T     96K    1.8T     0%    /backup
backup/data      1.8T     96K    1.8T     0%    /backup/data
storage                 449G     96K    449G     0%    /storage
storage/data    449G     96K    449G     0%    /storage/data

Networked Storage with NFS

Enable NFSv4 by adding the following services to /etc/rc.conf:


If you don’t have an /etc/exports file yet, you can create a blank one.

Start NFS without rebooting:

$ service nfsd start
Starting rpcbind.
Starting mountd.
Starting nfsd.

$ service nfsuserd start
Starting nfsuserd.

Sharing ZFS dataset:

zfs set sharenfs=on storage/data

This will share our dataset over NFS with the default options mentioned in zfsprops(8).

We can list all the custom options in a dataset like this:

$ zfs get -r -s local all storage/data
NAME          PROPERTY              VALUE                  SOURCE
storage/data  sharenfs              on                     local
storage/data  compression           on                     local
storage/data  atime                 off                    local

Or get the value for specific options:

$ zfs get sharenfs
backup        sharenfs  off       default
backup/data   sharenfs  off       default
storage       sharenfs  off       default
storage/data  sharenfs  on        local

Now we should be able to mount storage/data on another machine with an NFS client installed:

mount -t nfs $HOST:/storage/data /mnt/zdata

I haven’t gone through the necessary configuration for NFSv4, so my connection is getting demoted to NFSv3. This is okay for now because I’m the only user anyway and I’m connecting on a local network.

$ mount -vvv -t nfs $HOST:/storage/data /mnt/zdata/
mount.nfs: timeout set for Wed Jan 26 01:02:03 2022
%mount.nfs: trying text-based options 'vers=4.2,addr=,clientaddr='
mount.nfs: mount(2): Permission denied
mount.nfs: trying text-based options 'vers=4,minorversion=1,addr=,clientaddr='
mount.nfs: mount(2): Permission denied
mount.nfs: trying text-based options 'vers=4,addr=,clientaddr='
mount.nfs: mount(2): Permission denied
mount.nfs: trying text-based options 'addr='
mount.nfs: prog 100003, trying vers=3, prot=6
mount.nfs: trying prog 100003 vers 3 prot TCP port 2049
mount.nfs: prog 100005, trying vers=3, prot=17
mount.nfs: trying prog 100005 vers 3 prot UDP port 797

While I continue to set things up, I made /storage/data “word-writable” so I can actually start using the file server.2

chmod -R 777 /storage

Ultimately, I would like to use “ZFS over NFS” as my primary storage medium because it would keep everything in one place and let me access it from any computer.

Overall, ZFS is a really flexible filesystem and using ECC memory provides a lot of protection against data corruption. I can manage local and remote backups with zfs send and seamlessly add or replace drives by linking new zpools to my existing datasets.

Bonus: Creating my UFS scratch disk

(I’m using the serial number I got earlier and double-triple-checked my drive number!)

First, initialize the drive:

$ gpart create -s gpt ada2
ada2 created

$ gpart add -t freebsd-ufs -l 0000000012020907C404 -a 1M ada2
ada2p1 added

Then create the filesystem with TRIM enabled:

$ newfs -U -j -t -L scratch /dev/ada2p1
/dev/ada2p1: 122103.0MB (250066944 sectors) block size 32768, fragment size 4096
        using 196 cylinder groups of 625.22MB, 20007 blks, 80128 inodes.
        with soft updates
super-block backups (for fsck_ffs -b #) at: [...]

List the active filesystem options:

$ tunefs -p /dev/ada2p1
tunefs: POSIX.1e ACLs: (-a)                                disabled
tunefs: NFSv4 ACLs: (-N)                                   disabled
tunefs: MAC multilabel: (-l)                               disabled
tunefs: soft updates: (-n)                                 enabled
tunefs: soft update journaling: (-j)                       disabled
tunefs: gjournal: (-J)                                     disabled
tunefs: trim: (-t)                                         enabled
tunefs: maximum blocks per file in a cylinder group: (-e)  4096
tunefs: average file size: (-f)                            16384
tunefs: average number of files in a directory: (-s)       64
tunefs: minimum percentage of free space: (-m)             8%
tunefs: space to hold for metadata blocks: (-k)            6400
tunefs: optimization preference: (-o)                      time
tunefs: volume label: (-L)



Following the FreeBSD handbook’s advice of using 1 MiB alignments. Hopefully this is a good idea, I think letting gpart decide an alignment would be fine too.


It’s only temporary if it doesn’t work…

Last updated: 2022-01-26