subiquity isn't able to create btrfs subvolumes during installation

Yes, this is a gap.

Out of curiosity, would you be OK with supporting ZFS in a similar way as the desktop installer currently does, or do you prefer btrfs for some reason?

Michael, I guess you perfectly know why people choose ZFS over btrfs, and why other people choose btrfs over ZFS. Lack of proper btrfs support in Ubuntu Server installer wouldn't suddenly make admins switch from btrfs to ZFS - instead they will switch to Debian with familiar behavior.

So in my option right question is not "if btrfs users is Ok with ZFS?" but "for how long btrfs users willing to wait until subiquity implement familiar behavior for installation on btrfs before they will start transition to Debian?"

+1 for @ and @home by default. No wish to have affairs with ZFS.

+1 for @ and @home by default.

+1 for @ and @home by default.

You can just move to @ and @home manually after install.
My issue is a different one, Subiquity doesn't support installing on existing btrfs (I have RAID1 setup), it errors out with exit status 3.

My workaround was to
1. install the system on a separate drive
2. manually copy everything to new btrfs subvolumes /@ and /@home
3. make it bootable by booting from live ISO and running:

---
# be careful here, don't set the wrong device
DEVPATH=/dev/sda
DEVPARTPATH=/dev/sda2
MNTPATH=/mnt/sda2
MNTOPTS="-o subvol=@"

mkdir ${MNTPATH}
mount ${MNTOPTS} ${DEVPARTPATH} ${MNTPATH}
mount -t proc none ${MNTPATH}/proc
mount -o bind /dev ${MNTPATH}/dev
mount -o bind /sys ${MNTPATH}/sys

# get into the target system
DEVPATH=${DEVPATH} chroot ${MNTPATH} /bin/bash

# generate Grub2 config grub.cfg
grub-mkconfig

# generate Grub2 menu.lst file
update-grub2

update-initramfs -u -k all

# clean bootloader ; 512 (MBR) = 446 (bootloader) + 64 (part table) + 2 (signature)
dd if=/dev/zero of=$DEVPATH bs=446 count=1

# install Grub2 to MBR
grub-install --recheck $DEVPATH
---

I can just use windows. But this is not my option. Thanks. A full-fledged installer should support this simple things. Moreover a Debian installer had this support.

BTW Debian installer has not support installation on RAID1/0. And you can just first make an installation on usual partition and then add another one partition to the first one with 'btrfs device add' command and then perform a balancing with 'btrfs filesystem balance start -dconvert=raid1 -mconvert=raid1 /'.

Also seen in https://bugs.launchpad.net/subiquity/+bug/2024957 and https://bugs.launchpad.net/subiquity/+bug/2017893 .

This also breaks Timeshift, which expects subvolumes created for @/ and @/home. See https://github.com/linuxmint/timeshift/issues/232#issuecomment-1718289102 .