Re: undo make-bcache (was: Re: Can't mount an encrypted backing device)

[Coly Li <colyli@suse.de>]

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 <colyli@suse.de>:
>> 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