[$] Btrfs on zoned block devices

Zonedblock devices have some unfamiliar characteristics that result fromcompromises made in the name of higher storage density. They are dividedinto zones, some or all of which do not support random access for writeoperations. Instead, these "sequential" zones can only be written inorder, from the first block to the last. This constraint poses a newchallenge for filesystems, which are normally designed with the assumptionthat storage blocks can be written in any order. It is thus not surprisingthat zoned-device support in mainstream filesystems in Linux has been slowin coming; that is changing, though, with the additionof support for zoned block devices to Btrfs in Linux 5.12.