Re: [PATCH] btrfs-progs: check for minimal needed number of zones

On 12/05/2021 12:39, David Sterba wrote:

On Wed, May 12, 2021 at 04:53:05PM +0900, Johannes Thumshirn wrote:

quoted

In order to create a usable zoned filesystem a minimum of 5 zones is
needed:

- 2 zones for the 1st superblock
- 1 zone for the system block group
- 1 zone for a metadata block group
- 1 zone for a data block group

Some tests in xfstests create a sized filesystem and depending on the zone
size of the underlying device, it may happen, that this filesystem is too
small to be used. It's better to not create a filesystem at all than to
create an unusable filesystem.

Agreed, though there's no spare zone for relocation once any of them
becomes unusable (which is a known problem and can happen for any zone
count). Once this gets solved the limit will be increased accordingly.

Indeed, I'm planning to have something like a 'global' reserve zone for 
relocation. Hope to get this done before the cut for v5.14.