Re: Input/Output errors

[Kenny MacDermid <kenny.macdermid@gmail.com>]

On Tue, Feb 23, 2016 at 05:56:58PM -0800, Marc MERLIN wrote:
> On Tue, Feb 23, 2016 at 08:40:46PM -0400, Kenny MacDermid wrote:
> > I'm running btrfs on DM-Crypt Luks running on LVM.
> > 
> > Occasionally I get files that are unreadable for some period of time.
> > Attempting to read from them results in an 
> > 
> > Input/output error
> > 
> > Sometimes they'll come back on their own, and sometimes a scrub seems to
> > help, but sometimes I just have to delete them.
> > 
> > Nothing shows up in dmesg when these occur, and I can't predict which
> > files it will be, or what causes it.
> > 
> > It's currently happening running 4.4.1-2-ARCH, but I've seen the same
> > thing for many previous kernel versions.
> > 
> > Does anyone have any suggestions?
> 
> That's weird to say the least, you should at least get *something* in
> dmesg.
> And you are getting other error messages and btrfs kernel messages in
> your logs?
> 
> When whatever app you have that's trying to read them fails, I assume
> they also fail with cat or less?

I am getting other, normal btrfs messages. I'll include them at the end.
When it happens I get nothing at all in dmesg/logs.

And yes, cat will fail. I can move the file to another name though,
which I often do to get it out of the way.

They're mounted with:

rw,noatime,compress=lzo,ssd,discard,space_cache,autodefrag,inode_cache

issue_discards=1 is in lvm.conf, and discard in /etc/crypttab. (I'm now
reading that I probably shouldn't have it in fstab though and just run
fstrim.)

I don't know if this is related yet at all, but it /seems/ more likely
to happen after I delete a bunch of data. That could be a red herring
though.

When the file becomes readable again it's perfectly fine. Scrub never
finds any errors.

$ dmesg | grep -i btrfs
[   11.837137] Btrfs loaded
[   11.837403] BTRFS: device label root devid 1 transid 508963 /dev/dm-3
[   11.856203] BTRFS info (device dm-3): disk space caching is enabled
[   11.879366] BTRFS: detected SSD devices, enabling SSD mode
[   12.160267] BTRFS info (device dm-3): turning on discard
[   12.160272] BTRFS info (device dm-3): enabling auto defrag
[   12.160275] BTRFS info (device dm-3): enabling inode map caching
[   12.160277] BTRFS info (device dm-3): disk space caching is enabled
[   14.979093] BTRFS: device label home devid 1 transid 705779 /dev/dm-5
[   15.013978] BTRFS info (device dm-5): use ssd allocation scheme
[   15.013983] BTRFS info (device dm-5): turning on discard
[   15.013987] BTRFS info (device dm-5): enabling auto defrag
[   15.013989] BTRFS info (device dm-5): enabling inode map caching
[   15.013991] BTRFS info (device dm-5): disk space caching is enabled
[   15.100779] BTRFS error (device dm-5): could not find root 8
[   15.102889] BTRFS error (device dm-5): could not find root 8
[   15.105833] BTRFS error (device dm-3): could not find root 8
[   15.105838] BTRFS error (device dm-3): could not find root 8