Good morning Daniel,
On 3/30/20 10:09 PM, Daniel Jones wrote:
Hello Phil,
In particular, knowledge of the filesystem or nested structure (LVM?) present on the array will be needed to identify the real data offsets of the three mangled members.
I don't have the history of original creation, but I'm fairly certain
it was something straightforward like:
mdadm --create /dev/md0 {parameters}
sudo mkfs.ext4 /dev/md0
mount /dev/md0 /mnt/raid5
After the array was corrupted I needed to comment out the mount from
my fstab, which was as follows (confirming ext4):
/dev/md0 /mnt/raid5
ext4 defaults 0 0
Ok. This should be relatively easy, if a bit time consuming. Things we
know:
1) array layout, and chunk size: 512k or 1024 sectors
2) Active device #1 offset 261124 sectors.
3) The array had bad block logging turned on. We won't re-enable this
mis-feature. It is default, so you must turn it off in your --create.
Things we don't know:
1) Data offsets for other drives. However, the one we know appears to
be the typical you'd get from one reshape after a modern default
creation (262144). There are good odds that the others are at this
offset, except the newest one that might be at 262144. You'll have to
test four combinations: all at 261124 plus one at a time at 262144.
2) Member order for the other drives. Three drives taken three at a
time is six combinations.
3) Identity of the first drive kicked out. (Or do we know?) If not
known, there's four more combinations: whether to leave out or one of
three left out.
That yields either twenty-four or 96 different --create --assume-clean
combinations to test to find the one that gives you the cleanest
filesystem in a read-only fsck. (Do NOT mount! Even a read-only mount
will write to the filesystem. Only test with fsck -n.)
Start by creating partitions on all devices, preferably at 2048 sectors.
(Should be the default offered.) Use data offsets 259076 and 260100
instead of 261124 and 262144.
I recommend writing out all the combinations before you start and
keeping the fsck -n output from each until you have the final version
you want.
Yeah, I'd write a script to do it all for me, if your best guess
combination doesn't yield a good filesystem.
Cheers,
DJ
Phil
