Re: btrfs scrub: cancel + resume not resuming?

["Holger Hoffstätte" <holger@applied-asynchrony.com>]

On 1/9/20 11:03 AM, Sebastian Döring wrote:
> Maybe I'm doing it entirely wrong, but I can't seem to get 'btrfs
> scrub resume' to work properly. During a running scrub the resume
> information (like data_bytes_scrubbed:1081454592) gets written to a
> file in /var/lib/btrfs, but as soon as the scrub is cancelled all
> relevant fields are zeroed. 'btrfs scrub resume' then seems to
> re-start from the very beginning.
> 
> This is on linux-5.5-rc5 and btrfs-progs 5.4, but I've been seeing
> this for a while now.
> 
> Is this intended/expected behavior? Am I using the btrfs-progs wrong?
> How can I interrupt and resume a scrub?

Using 5.4.9+ (all of btrfs-5.5) and btrfs-progs 5.4 I just tried and
it still works for me (and always has):

$btrfs scrub start /mnt/backup
scrub started on /mnt/backup, fsid d163af2f-6e03-4972-bfd6-30c68b6ed312 (pid=25633)

$btrfs scrub cancel /mnt/backup
scrub cancelled

$btrfs scrub resume /mnt/backup
scrub resumed on /mnt/backup, fsid d163af2f-6e03-4972-bfd6-30c68b6ed312 (pid=25704)

..and it keeps munching away as expected.

TBH it's a bit odd that there is no "pause" - I'd expect cancel to be final,
but apart from that it seems to work.

-h