On Fri, Jul 19, 2019 at 10:10:46AM +1000, bob via luv-main wrote:
the RAID filing system. I have tried ddrescue which I
able to use to copy data from the main partition on the damaged disk
onto an old ntfs disk I had lying around but it is still unreadable
as the raid filesystem refuses to mount and I still can't see the
firstly, my sympathies. raid recoveries are not fun :-/
there's some stuff here, but it looks quite synology specific
if you are treating this as a generic linux recovery instead (probably
safer IMHO) then yup, ddrescue is the right way to go. hopefully ddrescue
didn't report many issues getting data off the drive?
first check that the ddrescue image is vaguely ok with eg.
losetup -P -r /dev/loop0 ddrescue.img
to see what it looks like read-only.
after that I would not touch the real disk again, or the orig ddrescue
image either. make a copy of a the ddrescue image you have, and
experiment with loopback mounts on that.
losetup -d /dev/loop0
cp ddrescue.img play.img
losetup -P /dev/loop0 play.img
and then see if you can force mdadm to accept eg. /dev/loop0p2 in
mdadm --examine ..
I don't know the exact recipe for this that'd work off the top of my
head, but it shouldn't be too hard.
if something does wrong then you can always start again with another cp
from ddrescue.img. you could do quick raid experiments with small
loopback filesystems and mdadm too.
another hint is that if the filesystem you store the images on supports
sparse files then you can likely save some space with cp --sparse=always
instead of cp.