Hi!

On Mon, 20 Dec 2021 at 16:45, Jorge Peixoto de Morais Neto
[off-list ref] wrote:

Is that experience from before Bullseye?  I heard that the Bullseye
installer has better Btrfs support.

This is my experience moving from ext4 to btrfs on several laptops,
desktops and servers. Probably your distro has the support right
enough for you, I don't know. If it doesn't, however, you can always
redo it the proper way afterwards.

Does Btrfs unsuitability to QEMU VM images relate exclusively to
synchronous write *performance*, or does it also harm SSD lifetime
(assuming nodatacow and raw format)?  I intend to give my VM a second
disk image.  One image will be on the SSD (holding system files) and the
other on the SATA HDD (holding user files).  The NVMe SSD is probably
fast enough that the VM will have overall good performance even with the
synchronous write slowness you mentioned; but would it excessively wear
the SSD?  Do I have to create an ext4 partition on the SSD just for the
QEMU VM disk image?

Sorry, I haven't got any spare SSDs to perform my tests on them.

I am aware Btrfs has official support for swap files (with some
restrictions), but is it reliable, efficient and light on the SSD
lifetime?  The Debian wiki recommends against swap file on Btrfs
(although some parts of Debian wiki are visibly outdated).

AFAIK kernel uses file swap as a list of extents on the disk not
accessing FS for the IO. Therefore, btrfs is perfectly OK for file
swap, provided the file is 'nodatacow'.