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I built a RAID5 array with 4 2Tb devices a few month ago.
- I used LVM2 to build partitions.
- I also used GRUB2.
- Finally I installed Debian.
For an unknown reason the RAID failed. The BIOS "see" only two devices.
I am aware that my RAID is lost.
For the two failed devices smart tool return nothing.

1) with the reduced RAID array:

  • is it possible to retrieve logical volumes and backup them ?
  • is it possible to separate them, I mean to have two devices and not one RAID of two devices, and retrieve data ?

2) When I try to boot with the two good devices, grub rescue takes the control.
The ls command gives:

(hd0) (hd0,msdos1) (hd1) (hd1,msdos1) (md/0)

ls .../boot gives unknown filesystem
ls (md/0) gives error disk 'md/0' not found.

3) I boot an old device and install on it the HDDsupertool application. This application detects the failed disk by the command: hddsupertool -d

ata1 - cff0 cf7e cfa0 1 wdc2003FYYS-02w0b1

But this application is complicate and I don't know if I could retrieve data.
Any ideas I could retrieve data or repair RAID ...

Thanks

  • The problem is, for a four-drive RAID five configuration, the data are striped across three disks, so you're going to be missing a third of everything. – DopeGhoti Feb 28 '16 at 17:54
  • I ask myself if really both disks are ko. the probability is low. that's why I search also a solution in this direction ... – Bertaud Feb 28 '16 at 18:07
  • It sounds like a problem with your BIOS or motherboard rather than a hardware failure of the drives themselves. If hddsupertool can see the 'failed' drive, then so can the linux kernel (try booting with a rescue CD or USB stick). If the kernel can see the drive, then the RAID array can be re-assembled and the data retrieved - (you should immediately copy the data to somewhere else!). I recommend installing all of the drives on another motherboard - or simply replacing your motherboard. – cas Feb 28 '16 at 23:37
  • I tried to boot an old hdd by moving it in each slot and the boot was always correct. hddsupertool sees it as an IDE disk, uses the direct io mode. I would see rather a problem with the s.m.a.r.t data (hddsupertool does not see them). – Bertaud Feb 28 '16 at 23:47
  • does blkid or lsblk show the drives? if yes, then the kernel sees them and the RAID array can be re-assembled (and the data copied!) as i mentioned earlier. – cas Feb 29 '16 at 10:32
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If you have a RAID5 device with 2 failed disks, you will only be able to recover bits and pieces of the device. In this case, ⅔ of the blocks would be recoverable. If there is some really important piece of data that you hope to recover and that's small enough to fit in a single RAID stripe, then with a fairly large amount of effort you can see if you can scan for it block-by-block (no guarantees), but that's about it. You will have little luck recovering any kind of intelligible filesystem. Sorry.

  • bad news. scan with hexdump ? – Bertaud Feb 28 '16 at 18:04
  • @Bertaud something like that :-( – Celada Feb 28 '16 at 18:06
  • Someone on internet used hexdump /dev/sda1 -C | grep 'LABELONE' : is it possible to find the beginning of an LV ? – Bertaud Feb 28 '16 at 18:10
  • Well, you'll have about a ⅔ chance of finding anything you look for, so yes, maybe. But what will you do once you find the beginning of one of the LVs? With ⅓ of its contents outright missing it will be too far gone to fsck or mount. – Celada Feb 28 '16 at 18:13

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