Hi Moritz, et al,
On 4/11/23 20:18, Wol wrote:
On 11/04/2023 20:47, John Stoffel wrote:
"Moritz" == Moritz Rosin <moritz.rosin@xxxxxxxxxxxx> writes:
Hey there,
unfortunately I have to admit, that I learned my lesson the hard way
dealing with software raids.
I had a raid1 running reliable over month using two 4TB HDDs.
Since I ran short on free space I tried to convert the raid1 to a raid5
in-place (with the plan to add the 3rd HDD after converting).
That's where my incredibly stupid mistake kicked in.
I followed an internet tutorial that told me to do:
mdadm --create /dev/md0 --level=5 --raid-devices=2 /dev/sdX1 /dev/sdY1
Ewww.
Please share the link to the tutorial so we can maybe shame that
person into fixing it. Or removing it.
See below. There's no reason why it shouldn't work, PROVIDED nothing has
happened to the mirror since you created it.
I learned that I re-created a raid5 array instead of converting the
raid1 :-(
Indeed. It would have sync'd every other chunk in opposite directions
to place "parity" in the right rotation, but otherwise equivalent to a
mirror.
Yeah, I think you're out of luck here. What kind of filesystem did
you have on your setup? Were you using MD -> LVM -> filesystem stack?
Or just a raw filesystem on top of the /dev/md? device?
I dunno. A two-disk raid-5 is the same as a 2-disk mirror. That raid-5
MAY just start and run and you'll be okay. You can try mounting it
read-only and see what happens ...
The odds of matching offsets depends entirely on how old the original
raid1 was.
Is there any chance to un-do the conversion or restore the data?
Has the process of creation really overwritten data or is there
anythins left on the disk itself that can be rescued?
If the conversion has overwritten the data, it will merely have
overwritten one copy of the data with the other.
Concur.
If you have any information on your setup before you did this, then
you might be ok, but honestly, I think you're toast.
It might be a bit of a forensic job, but no I don't think so. Do you
have that third 4TB HDD? If so, MAKE A BACKUP of one of the drives. That
way, you'll have three copies to play with to try and recover the data.
This.
As John says, please give us all the information you can. If you've just
put a file system on top of the array, you should now have three copies
of the filesystem to try and recover. I can't help any further here. but
all you have to do is track down the start of said filesystem, work out
where you tell linux to start a partition so it correctly contains the
filesystem, and then mount said partition. Your data should all be there.
The trick will be to determine the offset. Please share as much
information as possible as to the layering of the original setup,
preferable with the fstab contents if available.
Actually, you might be better off not copying onto drive 3. If you can
work out where your filesystem partition should start, create a
partition on drive 3 and copy the filesystem contents into said partition.
Or overlays with dmsetup.
I've cc'd a couple of people I hope can help, but basically, you need to
find out where in the raid array your data has been put, and then work
out how to access it. Your data SHOULD be recoverable, but you've got
some detective work ahead of you.
Your odds are decent. Again, share all the info you can.
Cheers,
Wol
Phil
