Rebuild only specific disks

[T4ke]

Hi everyone,
I have a general question about Unraid's Rebuild Process.
First of all about the situation:
I have 16 hard disks in my server.
8 are connected to the motherboard SATA controller, 8 more are connected to an Adaptec 71605 controller.

All hard disks are XFS formatted and encrypted.

Now last night I made a serious mistake:
In the course of a firmware update I wanted to flash to the Adaptec controller the headers of all hard disks connected to the controller were overwritten up to the offset FFFF. Why this happened, I can not explain.
I have not been able to find anything about whether others also had to make this experience in the course of a firmware update.
In any case, these hard disks are no longer recognized by Unraid since the LUKS header was obviously destroyed. The other still working disks have their LUKS header at offset 8000 so it would be within the erased offeset range (don't know if Unraid genereally places the LUKS header at offset 8000).
As I found out through my intensive research it's not possible to recover the LUKS header (or the data on that specific partition) without a binary header backup (which I don't have). Things I have already tried and and turned out not working:

 

• Search LUKS header using Hex Editor
• Clone LUKS header of another still working disk, hoping Unraid always uses the same master key within the array (which was not the case)
• Place a Loop Device on the LUKS device, starting at offset 8000.

 

Anyway, I resigned myself to the fact that the data of the 8 hard disks is lost in a direct or indirect way.

I do have a backup but it is no longer 100% up to date.

 

My question now is as follows:
Since I have two parity drives, would it be possible to recover at least two of the hard drives and leave the others "as it is" or does Unraid need the other drives to be intact to do this? If it's possible, how would I proceed here?

 

Many thanks in advance and a wonderful christmas season,

 

Robin

 

[itimpi]

35 minutes ago, T4ke said:

Unraid need the other drives to be intact to do this?

This unfortunately   
 

The rebuild process always involves successfully reading data from all disks except the ones being rebuilt to recover a drive.   This means the maximum number of drives that can be recovered is equal to the number of parity drives as long as the number of damaged/failed disks is equal to or less than the number of parity drives.   Unfortunately you have more damaged drives than parity drives.

[JorgeB]

If it was only the MBR that was missing/damaged you could rebuild one disk at a time, since the partition info is outside parity it would be recreated, I never used encryption, but pretty sure LUKS headers are inside the partition, so not possible to rebuild just one or two disks since the info needed to rebuild the LUKS heathers is missing from other disks.

[T4ke]

44 minutes ago, JorgeB said:

If it was only the MBR that was missing/damaged you could rebuild one disk at a time

 

how would I do that?

 

Thank you for your answers so far, I already feared this.

[JorgeB]

17 hours ago, T4ke said:

how would I do that?

If the problem was just the partition you could rebuild one disk at a time, like this:

https://forums.unraid.net/topic/84717-moving-drives-from-non-hba-raid-card-to-hba/

 

But offset FFFF covers the first 127 sectors, and Unraid partitions start on sector 64, offset (8000), which is where you mentioned the LUKS headers were, and that makes sense, they should be right after the partition start, so you'll be missing that info in the damaged disks.