On Thu, Feb 18, 2016 at 10:48:57PM -0800, Marc MERLIN wrote:

So, I have this:
├─nvme0n1p4   259:4    0    30G part  bcache                   8fd98dbd-4e87-4faa-8cec-d5f1e3910daa ae581b32-8c62-41a9-bfcf-ca8cec66e46a
│ └─bcache0   252:0    0   1.1T disk  crypto_LUKS              d6c98ca4-23b4-4aa3-819b-b384d4ac1b6a 
│   └─pool2   251:3    0   1.1T crypt btrfs       /mnt/btrfs_p 5ed9d54d-2f12-4735-85c2-e0445a316088 
├─sda7          8:7    0   1.1T part  bcache                   6d88cea7-6cfc-4d30-8cf5-8c8b216e019d 753dca8b-07
│ └─bcache0   252:0    0   1.1T disk  crypto_LUKS              d6c98ca4-23b4-4aa3-819b-b384d4ac1b6a 
│   └─pool2   251:3    0   1.1T crypt btrfs       /mnt/btrfs_p 5ed9d54d-2f12-4735-85c2-e0445a316088 


├─sda6          8:6    0    65G part  bcache                   21c07a2c-6ed2-42c2-aafb-8e1bbfa471a5 753dca8b-06
└─sdb1          8:17   0   1.8T part  bcache                   b324cfc4-a5ae-4888-ad6c-a5ba1002fdce 89ba6da8-01
  └─bcache1   252:1    0   1.8T disk  crypto_LUKS              b519d6ce-291a-4500-937e-a5957e6ece6b 
    └─pool3   251:4    0   1.8T crypt btrfs       /mnt/btrfs_p 5874cad5-d6dd-4b3d-a455-4e0ae2611f09 

bcache0 is fine
bcache1 ended up in a bad state, I'm not sure how.
No biggie, right, just delete/recreate/re-register sda6, except how?

https://www.kernel.org/doc/Documentation/bcache.txt
SYSFS - CACHE DEVICE:
says nothing about how I can free/release sda6

saruman:~# echo /dev/sda6 > /sys/fs/bcache/unregister
-su: /sys/fs/bcache/unregister: Permission denied
is not helpful, nothing in kern.log

echo 1 > /sys/fs/bcache/<uuid>/unregister