Re[6]: Filesystem sometimes Hangs

["Hendrik Friedel" <hendrik@friedels.name>]

Hello Chris,

thanks for your reply.

>>  >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.
Indeed:
grep btrfs
/dev/sdc2 on /srv/dev-disk-by-label-DockerImages type btrfs 
(rw,noatime,ssd,discard,space_cache,subvolid=5,subvol=/)
/dev/sdd2 on /srv/dev-disk-by-label-Daten type btrfs 
(rw,relatime,ssd,space_cache,subvolid=5,subvol=/)
/dev/sda1 on /srv/dev-disk-by-label-DataPool1 type btrfs 
(rw,noatime,space_cache,subvolid=5,subvol=/)

You can see, that for sdc2 and sdd2, "ssd" is in the mount options. For 
sdc2 discard is present. I have not added this myelf. But it is in 
fstab.
In fact, I got confused in my previous mail:
sdc is an ssd and not the drive that I was experiencing problems with 
(well: The system was slow when accessing sda1. I cannot exclude, that 
this was caused by sdc2.


>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.
Will do.
>
>>  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
>HDD?
See above. It was my mistake, thinking it sdc2 was the spinning disc.

>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.
Ok, will do.

Thanks,
Hendrik
>
>
>
>
>--
>Chris Murphy