Hi Anthony,
On 1/18/22 2:51 PM, anthony wrote:
You all know the story of how the cobbler's children are the worst shod,
I expect :-) Well, the superblock to my raid (containing /home, etc) has
disappeared, and I don't have a backup ... (well I do but it's now well
out of date).
Glitch when writing something else. Who knows.
So, a new hard drive is on order, for backup ...
Firstly, given that superblocks seem to disappear every now and then,
does anybody have any ideas for something that might help us track it
down? The 1.2 superblock is 4K into the device I believe? So if I copy
the first 8K ( dd if=/dev/sda4 of=sda4.img bs=4K count=2 ) of each
partition, that might help provide any clues as to what's happened to
it? What am I looking for? What is the superblock supposed to look like?
Well, I've gone to the kernel code for the structure definition a few
times, but never really got much out of it that mdadm -E didn't supply.
Those seem to be missing from your mail, at least for the still-working
drives....
Wait: they're gone from all three?
Secondly, once I've backed up my partitions, I obviously need to do
--create --assume-clean ... The only snag is, the array has been
rebuilt, so I doubt my data offset is the default. The history of the
array is simple. It's pretty new, so it will have been created with the
latest mdadm, and was originally a mirror of sda4 and sdb4.
A new drive was added and the array upgraded to raid-5, and I BELIEVE
the order is sdc4, sda4, sdb1 - sdb1 being the new drive that was added.
No mdadm -E at all?
Never ran lsdrv and tucked away the output?
Am I safe to assume that sdc4 and sda4 will have the same data offset?
What is it likely to be? And seeing as it was the last added am I safe
to assume that sdb1 is the last drive, so all I have to do is see which
way round the other two should be?
Not safe. But there's only six combinations.
At least the silver lining behind this, is that having been forced to
recover my own array, I'll understand it much better helping other
people recover theirs!
Cheers,
Wol
Phil
