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.. title: A quick ZFS overview on Linux .. date: 2020-01-27 .. slug: a-quick-zfs-overview-on-linux .. updated: 2020-01-27 .. status: published .. tags: misc, zfs, file system .. category: misc .. authors: Elia el Lazkani .. description: A overview of Linux on ZFS root .. type: text
I have, for years, been interested in file systems. Specifically a file system to run my personal systems on. For most people Ext4 is good enough and that is totally fine. But, as a power user, I like to have more control, more features and more options out of my file system.
I have played with most of file sytsems on Linux, and have been using Btrfs for a few years now. I have worked with NAS systems running on ZFS and have been very impressed by it. The only problem is that ZFS wasn't been well suppored on Linux at the time. Btrfs promissed to be the ZFS replacement for Linux nativetly, especially that it was backed up by a bunch of the giants like Oracle and RedHat. My decision at that point was made, and yes that was before RedHat's support for XFS which is impressive on its own. Recently though, a new project gave everyone hope. OpenZFS came to life and so did ZFS on Linux.
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Linux has had ZFS support for a while now but mostly to manage a ZFS file system, so I kept watching until I saw a blog post by Ubuntu entitled Enhancing our ZFS support on Ubuntu 19.10 – an introduction.
In the blog post above, I read the following:
We want to support ZFS on root as an experimental installer option, initially for desktop, but keeping the layout extensible for server later on. The desktop will be the first beneficiary in Ubuntu 19.10. Note the use of the term ‘experimental' though!
My eyes widened at this point. I know that Ubuntu has had native ZFS support since 2016 but now I could install it with one click. At that point I was all in, and I went back to Ubuntu.
Ubuntu on root ZFS
You heard me right, the Ubuntu installer offers an 'experimental' install on ZFS. I made the decision based on the well tested stability of ZFS in production environments and its ability to offer me the flexibility and the ability to backup and recover my data easily. In other words, if Ubuntu doesn't work, ZFS is there and I can install whatever I like on top and if you are familiar with ZFS you know exactly what I mean and I have barely scratched the ice on its capabilities.
So here I was with Ubuntu installed on my laptop on root ZFS. So I had to do it.
# zpool status -v
pool: bpool
state: ONLINE
status: The pool is formatted using a legacy on-disk format. The pool can
still be used, but some features are unavailable.
action: Upgrade the pool using 'zpool upgrade'. Once this is done, the
pool will no longer be accessible on software that does not support
feature flags.
scan: none requested
config:
NAME STATE READ WRITE CKSUM
bpool ONLINE 0 0 0
nvme0n1p4 ONLINE 0 0 0
errors: No known data errors
pool: rpool
state: ONLINE
scan: none requested
config:
NAME STATE READ WRITE CKSUM
rpool ONLINE 0 0 0
nvme0n1p5 ONLINE 0 0 0
errors: No known data errors
Note
I have read somewhere in a blog about Ubuntu that I should not run an upgrade on the boot pool.
and it's running on…
# uname -s -v -i -o Linux #28-Ubuntu SMP Wed Dec 18 05:37:46 UTC 2019 x86_64 GNU/Linux
Well that was pretty easy.
ZFS Pools
Let's take a look at how the installer has configured the pools.
# zpool list NAME SIZE ALLOC FREE CKPOINT EXPANDSZ FRAG CAP DEDUP HEALTH ALTROOT bpool 1,88G 158M 1,72G - - - 8% 1.00x ONLINE - rpool 472G 7,91G 464G - - 0% 1% 1.00x ONLINE -
So it creates a boot pool and a root pool. Maybe looking at the datasets would give us a better idea.
ZFS Datasets
Let's look at the sanitized version of the datasets.
# zfs list NAME USED AVAIL REFER MOUNTPOINT bpool 158M 1,60G 176K /boot bpool/BOOT 157M 1,60G 176K none bpool/BOOT/ubuntu_xxxxxx 157M 1,60G 157M /boot rpool 7,92G 449G 96K / rpool/ROOT 4,53G 449G 96K none rpool/ROOT/ubuntu_xxxxxx 4,53G 449G 3,37G / rpool/ROOT/ubuntu_xxxxxx/srv 96K 449G 96K /srv rpool/ROOT/ubuntu_xxxxxx/usr 208K 449G 96K /usr rpool/ROOT/ubuntu_xxxxxx/usr/local 112K 449G 112K /usr/local rpool/ROOT/ubuntu_xxxxxx/var 1,16G 449G 96K /var rpool/ROOT/ubuntu_xxxxxx/var/games 96K 449G 96K /var/games rpool/ROOT/ubuntu_xxxxxx/var/lib 1,15G 449G 1,04G /var/lib rpool/ROOT/ubuntu_xxxxxx/var/lib/AccountServices 96K 449G 96K /var/lib/AccountServices rpool/ROOT/ubuntu_xxxxxx/var/lib/NetworkManager 152K 449G 152K /var/lib/NetworkManager rpool/ROOT/ubuntu_xxxxxx/var/lib/apt 75,2M 449G 75,2M /var/lib/apt rpool/ROOT/ubuntu_xxxxxx/var/lib/dpkg 36,5M 449G 36,5M /var/lib/dpkg rpool/ROOT/ubuntu_xxxxxx/var/log 11,0M 449G 11,0M /var/log rpool/ROOT/ubuntu_xxxxxx/var/mail 96K 449G 96K /var/mail rpool/ROOT/ubuntu_xxxxxx/var/snap 128K 449G 128K /var/snap rpool/ROOT/ubuntu_xxxxxx/var/spool 112K 449G 112K /var/spool rpool/ROOT/ubuntu_xxxxxx/var/www 96K 449G 96K /var/www rpool/USERDATA 3,38G 449G 96K / rpool/USERDATA/user_yyyyyy 3,37G 449G 3,37G /home/user rpool/USERDATA/root_yyyyyy 7,52M 449G 7,52M /root
Note
The installer have created some random IDs that I have not figured out if they are totally random or mapped to something so I have sanitized them. I also sanitized the user, of course. ;)
It looks like the installer created a bunch of datasets with their respective mountpoints.
ZFS Properties
ZFS has a list of features and they are tunable in different ways, one of them is through the properties, let's have a look.
# zfs get all rpool NAME PROPERTY VALUE SOURCE rpool type filesystem - rpool creation vr jan 24 23:04 2020 - rpool used 7,91G - rpool available 449G - rpool referenced 96K - rpool compressratio 1.43x - rpool mounted no - rpool quota none default rpool reservation none default rpool recordsize 128K default rpool mountpoint / local ...
This gives us an idea on properties set on the dataset specified, in this case, the rpool root dataset.
Conclusion
I read in a blog post that the Ubuntu team responsible for the ZFS support has followed all the ZFS best practices in the installer. I have no way of verifying that as I am not a ZFS expert but I'll be happy to take their word for it until I learn more. What is certain for now is that I am running on ZFS, and I will be enjoying its features to the fullest.