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All: I ran ddrescue from a 1.5 TB input (corrupted) Windows external drive that was formatted NTFS to a 8 TB (uncorrupted) Western digital external drive that was formatted ext4. The 8 TB drive was empty at the start of ddrescue.

The 8 TB device (/dev/sdb) will not load. When I plug it into my desktop, I get:

exited with non-zero exit status 32: mount: wrong fs type, bad option, bad superblock on /dev/sdb1"

When I type lsblk, I get:

sdb      8:16   0   7.3T  0 disk 
└─sdb1   8:17   0   1.4T  0 part 

I load gdisk to repair the partition and get:

GPT fdisk (gdisk) version 1.0.1

Caution: invalid main GPT header, but valid backup; regenerating main header
from backup!

Caution! After loading partitions, the CRC doesn't check out!
Warning! Main partition table CRC mismatch! Loaded backup partition table
instead of main partition table!

Warning! One or more CRCs don't match. You should repair the disk!

Partition table scan:
  MBR: MBR only
  BSD: not present
  APM: not present
  GPT: damaged

Found valid MBR and corrupt GPT. Which do you want to use? (Using the
GPT MAY permit recovery of GPT data.)
 1 - MBR
 2 - GPT
 3 - Create blank GPT

Your answer: 

I assume I need to move forward with the MBR? So I press 1 -- then what? Should I press r (for recovery and transformation) and then f? I'm trying to figure it out from the gdisk man page (https://linux.die.net/man/8/gdisk).

It seems to me that I want to delete the GPT partition and just expand the MBR partition.I have NO data on the disk other than the 1.5 TB in /dev/sdb1.

Finally, I'd like to use the fill-mode of ddrescue to identify the corrupted files (https://www.gnu.org/software/ddrescue/manual/ddrescue_manual.html#Fill-mode). Will any of these changes to the partition table compromise the fill-mode procedure to find corrupted files?

  • Note that you can't use the whole disk if you use a MBR partition table on a 8 TB disk. MBR only supports up to 2 TB. You can use the MBR for recovery of the 1.5 TB partition, and you should, if the original disk was a non-GPT disk, but converting the big disk to GPT is a must once you start using partitions that go beyond the first 2 TB. – Johan Myréen Jul 5 '18 at 13:20
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    What's the exact command you used when running ddrescue? – Emmanuel Rosa Jul 5 '18 at 13:22
  • This is the command I issued: sudo ddrescue -f -n -v -v -v -v /dev/sdc /dev/sdb rescue.log – user584936 Jul 5 '18 at 18:39

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