On Sun, Dec 19, 2021 at 2:17 PM Forza [off-list ref] wrote:

You might benefit from a general data balance too because balancing is really a free space defragmentation.

Thanks for the reply, yeah, it probably would, but it would take a
long time and I'm trying to avoid it for now.

Space_cache=v2 mount option can help because it is more performant with free space fragmentation.

Already using v2.

Another option is to defragment the metadata and extent trees.

Example :
# btrfs fi defrag -v /media/backup/
WARNING: directory specified but recursive mode not requested: /media/backup WARNING: a directory passed to the defrag ioctl will not process the files recursively but will defragment the subvolume tree and the extent tree. If this is not intended, please use option -r .

You would have to do this for each subvolume. It can't be done for read-only snapshots though.

Filesystem only has read-only snapshots, so Iguess it won't help here.

Best,
Jorge Bastos