On Wed, Mar 31, 2021 at 8:03 AM Hendrik Friedel <hend...@friedels.name> wrote:

> >>[Mo Mär 29 09:29:21 2021] BTRFS info (device sdc2): turning on sync discard
> >
> >Remove the discard mount option for this file system and see if that
> >fixes the problem. Run it for a week or two, or until you're certain
> >the problem is still happening (or certain it's gone). Some drives
> >just can't handle sync discards, they become really slow and hang,
> >just like you're reporting.
> In fstab, this option is not set:
> /dev/disk/by-label/DataPool1            /srv/dev-disk-by-label-DataPool1
>         btrfs   noatime,defaults,nofail 0 2

You have more than one btrfs file system. I'm suggesting not using
discard on any of them to try and narrow down the problem.  Something
is turning on discards for sdc2, find it and don't use it for a while.

> How do I deactivate discard then?
> These drives are spinning disks. I thought that discard is only relevant
> for SSDs?

It's relevant for thin provisioning and sparse files too. But if sdc2
is a HDD then the sync discard message isn't related to the problem,
but also makes me wonder why something is enabling sync discards on a

Anway I think you're on the right track to try 5.11.11 and if you
experience a hang again, use sysrq+w and that will dump the blocked
task trace into dmesg. Also include a description of the workload at
the time of the hang, and recent commands issued.

Chris Murphy

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