Re: RAID 1 to RAID 5 failure

[Roy Sigurd Karlsbakk <roy@karlsbakk.net>]

> Didn't do a backup :-(

First mistake… *Always* keep a backup (or three)

> 
> Unmount everything:

No need - what you should have done, was just to grow the array by

Partition the new drives exactly like the old ones
mdadm --add /dev/md0 /dev/sd[cd]1 # note that sd[cd] means sdc and sdd, but can be written this way on the commandline
mdadm --grow --level=5 --raid-devices=4

This would have grown and converted the array to raid5 without any data loss.

> $ sudo mdadm --create /dev/md0 -a yes -l 5 -n 2 /dev/sda /dev/sdd

As earlier mentioned, this is to create a new array, not a conversion.

> So, my question is: Is there a chance to redo the array correctly
> without losing the information inside? Is it possible to recover the
> 'lost' partition that existed on RAID 1 to be able to do a convenient
> backup? Or the only chance is to have a correct disk alignment inside
> the array to be able to use photorec to recover the files correctly?

As mentioned, it doesn't look promising, but there are a few things that can be tried.

Your data may still reside on the sda1 and sdd1, but since it was converted to RAID-5, the data would have been distributed among the two drives and not being the same on both. Further growing the raid, would move the data around to the other disks. I did a small test here on some vdisks to see if this could be reversed somehow and see if I could find the original filesystem. I could - but it was terribly corrupted, so not a single file remained.

If this was valuable data, there might be a way to rescue them, but I fear a lot is overwritten already. Others in here (or other places) may know more about how to fix this, though. If you find out how, please tell. It'd be interesting to learn :)

PS: I have my personal notebook for technical stuff at https://wiki.karlsbakk.net/index.php/Roy's_notes in case you might find that interesting. There's quite a bit about storage there. Simply growing a raid is apparently forgotten, since I thought that was too simple. I'll add it.

So hope you didn't lose too much valuable data

Vennlig hilsen / Best regards

roy
--
Roy Sigurd Karlsbakk
(+47) 98013356
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I all pedagogikk er det essensielt at pensum presenteres intelligibelt. Det er et elementært imperativ for alle pedagoger å unngå eksessiv anvendelse av idiomer med xenotyp etymologi. I de fleste tilfeller eksisterer adekvate og relevante synonymer på norsk.