NAS-Upgrade; How I stopped worrying and learned to love ZFS

I have a Server in my living room that runs Arch Linux. I originally set up this server to provide a NAS. The NAS serves as a backup solution for the clients in my network, and also stores my media collection.

When I initially set it up, I had just one (Desktop!) HDD: A Seagate Barracuda with 8TB of storage. For the filesystem, I chose Btrfs at the time because I heard some good things about it, and looking through the features it seemed to do what I wanted. But the longer I used it, the more problems creeped up. It doesn’t have native filesystem encryption, so I had to use LUKS. It supports Quotas, but doesn’t have a good way of displaying how much storage a specific subvolume/snapshot actually uses. It supports snapshots, but not too many of them. I also thought that subvolumes were very neat, so I created a lot of them to give each “application” a unique path that I tried to cram into the FHS-Philosophy. This caused more trouble than it solved though, because now I had a lot of different paths that I had to write down. I also made a bash script to mount all of these different subvolumes, and had to frequently look inside this script to keep all of the paths and subvolumes together. And with every Service I added, I needed to update this mounting script. This wasn’t really hard or complicated, but very annoying.



echo "Opening disk"
sudo cryptsetup open "$DISK1" "$CNAME" || echo 'failed'

echo "Mounting btrfs root"
sudo mount "/dev/mapper/$CNAME" "$ROOT_PATH/$CNAME" -o compress=zstd,autodefrag
|| echo 'failed'

echo "Mounting btrfs subvol 'jellyfin'"
sudo mount "/dev/mapper/$CNAME" "$NAS_ROOT/$JELLYFIN" -o
compress=zstd,autodefrag,subvol="/$JELLYFIN" || echo 'failed'

echo "Mounting btrfs subvol 'backup/biggs'"
mount "/dev/mapper/$CNAME" "$NAS_ROOT/$BACKUP_ROOT/biggs" -o
compress=zstd,autodefrag,subvol="/$BACKUP_ROOT/biggs" || echo 'failed'

echo "Mounting nextcloud subvol"
mount "/dev/mapper/$CNAME" "/var/nextcloud" -o
compress=zstd,autodefrag,subvol="/nextcloud" || echo 'failed'

echo "Mounting XXX subvol"
mount "/dev/mapper/$CNAME" "/var/www/" -o
compress=zstd,autodefrag,subvol="/tiktok" || echo "failed"

The script I used. It’s a bit of a mess.

I also created another script to automate snapshot creation. This was to protect the files on my SMB shares. If you delete a file from an SMB share on the client side, it’s gone. With this, I would have a chance to restore things if they were accidentally deleted. This made listing the subvolumes a complete shitshow, because the list was completetely cluttered with the snapshots. So a lot of Btrfs tools were just not working very well in my situation and I had to rely on scripts, both self-written and third-party.

The Move

That’s why I decided to move to ZFS. In this article, I will take you on the journey I faced to do this. I decided to this at the same time that I did a major hardware upgrade. Up to that point I just had one Desktop HDD. I decided to replace it with 3 WD Reds, each 8 TB in size. I will be running these in RAIDZ, an improved version of RAID5 that removes the write hole (a general problem in RAID 5, something Btrfs hasn’t been able to solve yet). It is also generally very efficient.

So, how will we go about this whole thing? There are 2 options:

Option 1 would be to replace all the Btrfs subvolumes with the ZFS equivalent (Datasets) and mount them at the exact same locations. The advantage would be that I don’t have to reconfigure the applications that use the storage. The disadvantage would be that my services would be down while the data transfers (and for over 5 TB, that would take a while).

Option 2 would be to mount both volumes, transfer the data and reconfigure the applications after the transfer is complete. The advantage here would that I would just have very short interruptions in service.

I decided to go for option 2. This has the other advantage that it forces me to organise the data in a different way, which is hopefully more sensible than scores of subvolumes that mount to different folders somewhere in the hierarchy.

First I had to decide how I wanted to install ZFS. If you don’t know about this problem, here’s a short explainer. ZFS uses a free software license, the CDDL This is a so-called copyleft license (a license which restricts using the code for proprietary software). One problem with this is that it is incompatible with the GPL. This means ZFS can’t be distributed with the Linux kernel. There is a third-party kernel module, called zfsonlinux, which we will be using. For Arch Linux, there are a few options of getting this kernel module. The recommended way of getting it is by installing a patched kernel that includes the module. The advantage is that this is the easiest solution, and installation/upgrade (which, for all intents and purposes, is always the same in Arch!) is very fast and not any different to upgrade a normal kernel. The disadvantage is that I have to wait for the maintainers to release new versions of the modified kernel. This can sometimes take months. Since I want to keep this server very up to date (and close to upstream) for security reasons, I didn’t like this option very much. The other option would be to use DKMS. This recompiles the module into the kernel every time there is a kernel update. Although the update takes slightly longer, this has the advantage of not having to wait for the maintainers to release a new patched kernel. The DKMS version is installed with the following command: pacman -S zfs-dkms linux-headers. After installing, we can start to configure ZFS.

ZFS Configuration

First we create a pool for our hard drives. Zfs-on-linux recommends using device ids when creating pools that are smaller than 10 devices. The device ids on Arch Linux can be found by showing the contents of /dev/disk/by-id.

lrwxrwxrwx 1 root root  9 Jun 26 13:53 ata-Intenso_SSD_Sata_III_AA000000000000016985 -> ../../sda
lrwxrwxrwx 1 root root 10 Jun 26 13:53 ata-Intenso_SSD_Sata_III_AA000000000000016985-part1 -> ../../sda1
lrwxrwxrwx 1 root root 10 Jun 26 13:53 ata-Intenso_SSD_Sata_III_AA000000000000016985-part2 -> ../../sda2
lrwxrwxrwx 1 root root 10 Jun 26 13:53 ata-Intenso_SSD_Sata_III_AA000000000000016985-part3 -> ../../sda3
lrwxrwxrwx 1 root root  9 Jun 26 13:53 ata-WDC_WD80EFBX-68AZZN0_VRG0M7DK -> ../../sdc
lrwxrwxrwx 1 root root  9 Jun 26 13:53 ata-WDC_WD80EFBX-68AZZN0_VRG8G6LK -> ../../sdb
lrwxrwxrwx 1 root root  9 Jun 26 13:53 ata-WDC_WD80EFBX-68AZZN0_VRG8ZJNK -> ../../sdd

In my case, this is /dev/sdb, /dev/sdc, and /dev/sdd. Using the device ids has the advantage that Linux changes the “classic” identifiers (sd[a-z]) if the boot order is different. So adding more disks, or just a USB drive, can change these. This is obviously something we want to avoid. So, to create our pool we use the following command:

zpool create -f -m /media/ zfsnas raidz ata-WDC_WD80EFBX-68AZZN0_VRG0M7DK ata-WDC_WD80EFBX-68AZZN0_VRG8G6LK ata-WDC_WD80EFBX-68AZZN0_VRG8ZJNK

If the command is successful, there should be no output. We can check the status of our pool with zpool status. The output should look like this:

  pool: zfsnas
 state: ONLINE

        NAME                                   STATE     READ WRITE CKSUM
        zfsnas                                 ONLINE       0     0     0
          raidz1-0                             ONLINE       0     0     0
            ata-WDC_WD80EFBX-68AZZN0_VRG0M7DK  ONLINE       0     0     0
            ata-WDC_WD80EFBX-68AZZN0_VRG8G6LK  ONLINE       0     0     0
            ata-WDC_WD80EFBX-68AZZN0_VRG8ZJNK  ONLINE       0     0     0

errors: No known data errors

So the pools are automatically imported on boot we need to enable 2 systemd services.

systemctl enable zfs-import-cache
systemctl enable

After that, we want to create datasets. These look like folders, but allow us to use other features, like mounting them under a different path and setting quotas. We create these datasets with zfs create <nameofzpool>/<nameofdataset>. In our case we also want to enable encryption. So the command looks like this

zfs create -o encryption=on -o keyformat=passphrase zfsnas/cryptset

ZFS asks us for a passphrase, which we then need to enter twice. After that we can start to create datasets for our different services. In my case, I have one dataset for my Nextcloud server, one for my SMB NAS, and one for the backups of my different clients. We also set quotas for each dataset.

zfs create zfsnas/cryptset/smb
zfs create zfsnas/cryptset/nextcloud
zfs create zfsnas/cryptset/backup
zfs set quota=8TB zfsnas/cryptset/smb
zfs set quota=200GB zfsnas/cryptset/nextcloud
zfs set quota=4TB zfsnas/cryptset/backup

After we have prepared the datasets, we transfer everything from the old disk to the new array. I’m doing this with rsync.

Reconfiguring Services

After transferring everything, we need to reconfigure our services. The one I was most afraid of was nextcloud. There is this help article that begins with this scary looking disclaimer:

First of all: Changing data directory after installation is not officially supported. Consider re-installing Nextcloud with new data directory, if you did not use it too much/added users/created shares/tags/comments etc.

That doesn’t inspire much confidence. The problem is that NC stores information about all files in its database. So this database to be either manually updated (error-prone) or rebuilt (losing basically all metadata like shares, comments, etc). I decided to do the second one, since I’m not a DBA by any stretch of the imagination, and I didn’t have many shares. If someone gets their data access cut off, they’ll complain anyway. Then I’ll be informed and can create a new share.

The first thing I did was change the location of the data directory. To do this, we need to change /etc/webapps/nextcloud/config.php. It contains a variable called datadirectory. After I changed this variable, I ran occ maintenance:repair for good measure. To my surprise, this was all that I needed. All files (and share links) were there. For Samba, I just changed the config (smb.conf) to the new location.

After that, everything worked. I’m looking forward to the new NAS, and I hope I will lose some of the hassle I had with Btrfs.