/dev/bcache* missing after reboot

/dev/bcache* missing after reboot

[Thierry De Leeuw]

Hi,

Running Linux 3.12.1. I have disk /dev/sda2 with LVM that has, amongst
other, lvHome as a bcache device, and the cache resides on /dev/sdb1

My PC hung and I had to do a forced shutdown.

Now the /dev/bcache0 (and so on) do not appear anymore.

The LVM is available (I can see /dev/mapper/vgData_lvHome), when I do a
bcache-super-show /dev/mapper/vgData_lvHome I get
sb.magic ok
ssb.first_sector 8 [match]
sb.csum xxxxx [match]
ssb.version 1 [backing device]

dev.label (empty)
dev.uuid xxxxx
dev.sector_per_block 8
dev.sector_per_bucket 1024
dev.data.first_sector 16
dev.data.cache_mode 1 [writeback]
dev.data.cache_state 2 [dirty]

cset.uuid yyyyyyy (note that it matches the entry in /sys/fs/bcache)

similar stuff for the other logical volumes so looks like the header is ok.

dmesg reports only the following entries about bcache
bcache: bch_journal_replay() journal replay done, 46 keys in 17 entries seq
973143
bcache: register_cache() registered cache sdb1

note that the same replay message is reported at each reboot.

/dev/block has no bcache* entries

looking at /sys/fs/bcache/yyyyyy
what seems suspicious to me is that the cache_available_percent is at 100
and dirty data is at 0 is it because it is not "connnected" to the backing
devices?

What can I do now to recover from this situation/help providing you
information to determine the problem and hav my disk back?

Thanks!

Thierry

Re: /dev/bcache* missing after reboot

[Matthias Ferdinand]

[already sent 2 days ago, but did not appear on the list]

On Mon, Dec 02, 2013 at 11:36:47PM +0100, Thierry De Leeuw wrote:
> Hi,
> 
> Running Linux 3.12.1. I have disk /dev/sda2 with LVM that has, amongst
> other, lvHome as a bcache device, and the cache resides on /dev/sdb1
> 
> My PC hung and I had to do a forced shutdown.
> 
> Now the /dev/bcache0 (and so on) do not appear anymore.

Perhaps you need to re-register / re-attach the backing device to the
caching device, something like 

   echo /dev/dm-xx > /sys/fs/bcache/register
   echo yyyyyyy > /sys/devices/virtual/block/dm-xx/bcache/attach   

If that does not help, you can try to force starting the bcache backing
device without the caching device (might give you serious fs damage with
writeback):

  echo "1" > /sys/devices/virtual/block/dm-xx/bcache/running

But since you are using LVM, you might want to create a snapshot of the
backing device LV before doing this, just in case.

Regards
Matthias