Using TestDisk to recover partitions, partition tables and boot sectors

TestDisk Step By Step - CGSecurity

Recently I had an issue with a MDX1000 external array and RedHat Enterprise Linux 5.4 where after I installed the OS and formatted /dev/sda to be a volume group the OS could not find the partition table for /dev/sdb. I wasn't too concerned during the installation process because I wasn't using that disk anyway but I definitely wanted to keep the 1.7TB partition since it had a lot of data on there that I did not want to recover from tape. Once the install was done, I was unable to mount /dev/sdb1 and a fdisk -l was not showing any partitions on the disk - this obviously was bad. To further compound matters, the total size of this array was 3.9TB which fdisk could not handle since it was larger than 2.2TB and I needed to use parted to try to get it work.

Once I got into parted, I discovered that the partition table was corrupted and needed to be rebuilt. I then found the utility testdisk which will work on Windows or Linux and does a great job of allowing you to find lost partitions and backup superblocks on the disk. I had the software recreate the partition table and set it to a EFI disk which allowed larger than 2.2TB disks and then it was able to find the lost partition with all of my data intact. I wrote the new partition table to disk and rebooted the server and was then able to successfully mount and use /dev/sdb1 just as it was before the 64 bit "upgrade" of the server.

I have not personally tried this yet on Windows or another flavor of Unix but I am now a big believer in this tool when all seems lost. And you can't beat the price: free.