[$] Btrfs on zoned block devices

Zoned
block devices have some unfamiliar characteristics that result from
compromises made in the name of higher storage density. They are divided
into zones, some or all of which do not support random access for write
operations. Instead, these 'sequential' zones can only be written in
order, from the first block to the last. This constraint poses a new
challenge for filesystems, which are normally designed with the assumption
that storage blocks can be written in any order. It is thus not surprising
that zoned-device support in mainstream filesystems in Linux has been slow
in coming; that is changing, though, with the addition
of support for zoned block devices to Btrfs in Linux 5.12.