Hello Shaun,

Monday, August 28, 2017, 11:00:02 AM, you wrote:

I need to recover a file from a bcache disk that won't mount, the
underlying fs is btrfs. I'd like to read the btrfs partition directly
by skipping the bcache data with dd skip=#, but I need to know how
much data to skip. Can anyone help me out?

Bcache tools include a program called bcache-super-show, it shows various
values from the cache or backing device superblock. In particular, there is
the "dev.data.first_sector" value which is what you want.

In my case, it shows:

dev.data.first_sector   16

Which means that the underlying data begins from 16-sector (8-kilobyte) offset
of the backing device.

Pavel Goran