=== filesystems, and which one backs Docker (the one NOT to fill) ===
Filesystem                        Mounted on                   1B-blocks        Avail
/dev/nvme0n1                      /mnt/felhom-drives/hdd_1 1006980812800 949296590848
/dev/mapper/pve-vm--9201--disk--1 /var/lib/felhom            73793978368  57945436160
/dev/mapper/pve-vm--9201--disk--1 /var/lib/docker            73793978368  57945436160
/dev/mapper/pve-vm--9201--disk--1 /mnt/sys_drive             73793978368  57945436160

=== fallocate available? (instant, metadata only, instantly reversible) ===
/bin/fallocate
yes
