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Today I bought a 128MB SSD disk, installed it, then installed bcache-tools. After attempting to access the device I got these errors:

root@dev:/sys/block/sda/bcache# make-bcache -B /dev/sdb1 /dev/sdb1 -C /dev/sda

Can't open dev /dev/sda: Device or resource busy





root@dev:/sys/block/sda/bcache# fdisk /dev/sda



Welcome to fdisk (util-linux 2.27.1).

Changes will remain in memory only, until you decide to write them.

Be careful before using the write command.



/dev/sda: device contains a valid 'bcache' signature; it is strongly recommended to wipe the device with wipefs(8) if this is unexpected, in order to avoid possible collisions



Device does not contain a recognized partition table.

Created a new DOS disklabel with disk identifier 0xfef282bc.



Command (m for help): q



root@dev:/sys/block/sda/bcache# wipefs -a /dev/sda

wipefs: error: /dev/sda: probing initialization failed: Device or resource busy

root@dev:/sys/block/sda/bcache# 

So I have the following questions:

• Why did bcache started to use my SSD disk (/dev/sda) without even asking me for permission? That's a lot of disrespect to the authority.


• How do I disable bcache so I can properly format the devices, they are not formatted yet.

This is the output of ls -l in bcache devices:

root@dev:/sys/block/sda/bcache# ls -l

total 0

-r--r--r-- 1 root root 4096 Apr 26 18:47 block_size

-r--r--r-- 1 root root 4096 Apr 26 18:47 btree_written

-r--r--r-- 1 root root 4096 Apr 26 18:47 bucket_size

-rw-r--r-- 1 root root 4096 Apr 26 18:47 cache_replacement_policy

--w------- 1 root root 4096 Apr 26 18:47 clear_stats

-rw-r--r-- 1 root root 4096 Apr 26 18:47 discard

-r--r--r-- 1 root root 4096 Apr 26 18:47 io_errors

-r--r--r-- 1 root root 4096 Apr 26 18:47 metadata_written

-r--r--r-- 1 root root 4096 Apr 26 18:47 nbuckets

-r--r--r-- 1 root root 4096 Apr 26 18:47 priority_stats

lrwxrwxrwx 1 root root    0 Apr 26 18:47 set -> ../../../../../../../../../../fs/bcache/b9d9517a-a606-4ac2-86dc-3399e9678381

-r--r--r-- 1 root root 4096 Apr 26 18:47 written

root@dev:/sys/block/sda/bcache# pwd

/sys/block/sda/bcache

root@dev:/sys/block/sda/bcache# 

.

root@dev:/sys/fs/bcache# ls -l

total 0

drwxr-xr-x 7 root root    0 Apr 26 19:00 b9d9517a-a606-4ac2-86dc-3399e9678381

--w------- 1 root root 4096 Apr 26 19:00 register

--w------- 1 root root 4096 Apr 26 19:00 register_quiet

root@dev:/sys/fs/bcache# 

bcache doesn't do this. Either the disk you purchased wasn't clean and already contained a bcache superblock upon unboxing (so it may be a returned drive that wasn't wiped properly), or the first command you ran was fishy: It has /dev/sdb1 twice on the command line which may have confused the command and it already created the superblock and attached /dev/sdb1.

To get rid of it, detach the backing device:

# echo 1 >/sys/block/sdb/sdb1/bcache/detach

Then unregister the cache:

# echo 1 >/sys/fs/bcache/b9d9517a-a606-4ac2-86dc-3399e9678381/unregister

Now, instantly wipe it before udev reregisters it:

# wipe -a /dev/sda

Do not be confused that /dev/sdb1 still shows up as under control of bcache. It doesn't hurt and you can access it through /dev/bcache0. It's not attached to a cache and thus doesn't benefit from any caching, it works in pass-through mode until you re-attach it to a cache manually:

# echo CACHE_SET_ID >/sys/block/sdb/sdb1/bcache/attach

In that case, you create a cache device only, then attach any disk to it (with the above command following this one):

# make-bcache -C CACHE_DEV