btrfs recovery - howto?

[ghaspias]

My xbian system, in an external usb hd, is in an unbootable state, and I think it is just a problem with btrfs. Since I have important work backed up in the system partition, a reinstall is not possible.
Usually, even if it is not bootable, I would have no problem pluging that disk in another linux system (or just boot xbian from sdcard) to recover the data. But when I connect that hd to either a laptop linux system (Fedora 21 live) or a fresh xbian running on RPi B+, both crash with kernel panics!

So, is it safe to try to recover this btrfs file system on a different (laptop) linux system? Does the different compression (I think I have lzo, but I'm not quite sure -- how to check it?) affect the prospect of normal recovery?

Thanks for any suggestion.

[ghaspias]

(19th Apr, 2015 04:27 AM)ghaspias Wrote:  My xbian system, in an external usb hd, is in an unbootable state, and I think it is just a problem with btrfs. Since I have important work backed up in the system partition, a reinstall is not possible.
Usually, even if it is not bootable, I would have no problem pluging that disk in another linux system (or just boot xbian from sdcard) to recover the data. But when I connect that hd to either a laptop linux system (Fedora 21 live) or a fresh xbian running on RPi B+, both crash with kernel panics!

So, is it safe to try to recover this btrfs file system on a different (laptop) linux system? Does the different compression (I think I have lzo, but I'm not quite sure -- how to check it?) affect the prospect of normal recovery?

Thanks for any suggestion.

After some (not very extensive) research, I still can not mount my btrfs xbian partition (on external usb HDD) in writable mode. I have been trying to access that filesystem using an Ubuntu 15.04 live iso, as well as a Fedora 22 live and both xbian-stable and xbian-latest fresh sdcard installs. It does mount, but in just a few seconds triggers kernel bugs and the system becomes unresponsive.
Still, I have found that I can recover (apparently all of) my data using btrfs-restore. The main issue I had with this approach is that I was not able to create a regex to exclude some paths (using --path-regex) and I have not enough free space to restore everything, from all different snapshots. Anyway, using meld diff viewer to compare @/ and a previous snapshot, it seems that @/ is ok, and I was able to come up with a regex to restore only from a specified snapshot or even a specified subpath, to recover my /etc/, /var/log/ and /opt/.
Later I found that I could mount my filesystem in read-only mode, using
mount -o ro,recovery /dev/sdc4 /mnt
Even the 'recovery' flag seems to be unnecessary.
So, this should let me backup anything I want.

I am still trying th find how to
a) get my filesystem to mount read/write (ideal case)
b) create a new clean install of xbian, in the same usb partition, without touching the remaining partitions, and without being subject to the same problem again...