Subiquity creates far too many zfs file systems

[Hadmut Danisch]

I just installed a Xubuntu machine (23.10) with subiquity, choosing ZFS as a root file system.

Just to install a simple Xubuntu I had no less then two zpools and 25 ZFS file systems right after installation.

Besides the fact, that this is a waste of space (even in ZFS, every file system occupies some space) and slows the system significantly down, since every file mv beyond these borders has to be turned into a copy operation (and thus occupies additional disk space once snapshots exist), it jams the system and overwhelmes the admin with an avalanche of file systems, some of them really useless.

Furthermore, it counterfights the intention to have a roll back for the system, since you really need to synchronize all snapshots (and technically can't have several filesystems snapshot' at exactly the same time).

This overload of ZFS filesystems does not make any sense (at least, no sense I am able to recognize after working intensively and permanently with ZFS for about 10 years), and I do not see what purpose it should have to distribute parts of the system onto different file systems, especially things like having /usr and /var/lib/dpkg on different filesystems (and thus different snapshots), since /var and /usr *must* match the state described by /var/lib/dpkg/info/* and apt cache. While it does make some sense to have things like LXD on a separate ZFS file system, having /usr and /var/lib/dpkg/info on different ones is a strong wish for a broken inconsistent system.

Fundamentally, an clean and simple installation should come with just one ZFS file system, i.e. the root filesystem on /. Maybe /tmp and /home would be good for a second one, especially if Ubuntu was able to create a fresh install and leave /home intact or even allow to have different Ubuntu installations/versions to choose from during boot while sharing /home or maybe /usr/local.

It does not make much (which?) sense to have two distinct zpools either. If it's for encryption: ZFS encryption allows to encrypt file systems and their childred, not just complete zpools.

However, all these extra file systems should only be offered as a option during installation, part of the manual installation process.

In my eyes, this is merely unusable and looks as if someone not really experienced more or less just used the examples section of subiquity, but never actually worked with all that overhead.

Which is sad, since ZFS is one of the best filesystems (if not the best) Linux currently has to offer.

Proposal:

Create just a single ZFS for /, and leave all others to the admin's choice during installation.

regards