Hi My original message was sent (and rejected) 4 days ago because it was in HTML (whoops). Here's my original e-mail with updates : I've got an Ubuntu machine with an mdadm RAID array on level 6. The RAID-6 array consists of 10 drives and has been running for about 3 years now. I recently upgraded the drives in the array from 1TB units to 2TB units. The drive on which the OS sat died a few days ago, so I installed a new OS drive and then installed Ubuntu Server on it. On reboot the machine hung on a black screen with a white flashing cursor. So I went back into the Ubuntu Setup and installed grub to all of the drives in the raid array (except two) [wow, this was such a stupid move]. I then rebooted the machine and it successfully booted into Ubuntu Server. I set about restoring the configuration for the raid array... only to be given the message "No Superblock Found" (more or less). Each element in the array was used directly by mdadm (so /dev/sda, not /dev/sda1). I see that the superblock is stored within the MBR region on the drive (which is 512bytes from the start of the disk), which would explain why the superblocks were destroyed. I haven't been able to find anything regarding a backup superblock (does something like this exist?). I have now started using a script that tries to re-create the array by running through the various permutations available... it takes roughly 2.5 seconds per permutation/iteration and there are just over 40 000 possibilities. The script tests for a valid array by trying to mount the array as read only (it's an XFS file system). I somehow doubt that it will mount even when the correct combination of disks is found. [UPDATE] : It never mounted. So... I have an idea... The array has a hole bunch of movie files on it and I have exact copies of some of them on another raid array. So I was thinking that if I searched for the start of one of those files on the scrambled array, I could work out the order of the disks by searching forward until I found a change. I could then compare the changed area (probably 128KB/the chunk size forward) with the file I have and see where that chunk lies in the file, thereby working out the order. [UPDATE] : Seeing as the array never mounted, I have proceeded with this idea. I took samples of the start of the video file and provided them to Scalpel as needles for recovery. After two days of searching, Scalpel located the starts of the various segments in the raid array (I re-created the raid array with the drives in random order). I then carved (using dd) 3MBs out of the raid array that contains all the samples handed to scalpel originally (plus a bit more). So now I have to find segments of the start of the intact file in the carved out data from the raid array. It would be really useful if I knew the layout of the array : If the chunk size of the array is 128KB, does that mean that the file I carved will be divided up into segments of contiguous data, each 128KBs in length ? or does it mean that the length of contiguous data will be 16KB ( 128 KB / 8 drives ) ? Do these segments follow on from each other without interruption or is there some other data in-between (like metadata? I'm not sure where that resides). Any explanation of the structure of a raid6 array would be greatly appreciated, as well as any other advice (tools, tips, etc). Thanks :) Aaron (24) South Africa -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
