On 2020/1/13 8:44 下午, Jens-U. Mozdzen wrote:

Hi Coly,

jumping in here, because I was looking for a way to revert from bcache
to plain device:

Zitat von Coly Li [off-list ref]:

quoted

The super block location of the backing disk is occupied by bcache. You
cannot mount the file system directly from the backing disk which is
formated as bcache backing device [...] (bcache offset all I/Os on
bcache device 4KB behind the requesting
LBA on backing disk).

Assuming that no caching device is associated with a backing device (so
the backing device is "clean" as in "containing all data blocks with the
current content"), could one convert the content of a backing device to
a "non-bcached device" by removing the first 4096 octets of the backing
device content?

Something like "dd if=backingdev of=newdev skip_bytes=4096 ..."?

Hi Jens-U,

you may try dmsetup to setup a linear device mapper target, and the map
table just skipping the first 4KB (bcache superblock area). If you are
lucky, I mean the real file system is not corrupted, the created device
mapper target can be mounted directly.


-- 

Coly Li