Re: [PATCH v4 08/13] btrfs:zoned: make sb for npo2 zone devices align with sb log offsets

Johannes Thumshirn
2022-05-17T06:51:52Z

On 16/05/2022 18:55, Pankaj Raghav wrote:
> Superblocks for zoned devices are fixed as 2 zones at 0, 512GB and 4TB.
> These are fixed at these locations so that recovery tools can reliably
> retrieve the superblocks even if one of the mirror gets corrupted.
>
> power of 2 zone sizes align at these offsets irrespective of their
> value but non power of 2 zone sizes will not align.
>
> To make sure the first zone at mirror 1 and mirror 2 align, write zero
> operation is performed to move the write pointer of the first zone to
> the expected offset. This operation is performed only after a zone reset
> of the first zone, i.e., when the second zone that contains the sb is FULL.

Hi Pankaj, stupid question. Npo2 devices still have a zone size being a
multiple of 4k don't they?

If not, we'd need to also have a tail padding of the superblock zones, in order
to move the WP of these zones to the end, so the sb-log states match up.