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Saving a 2TB GPT exFAT filesystem

Posted: 02 Aug 2012, 17:38
by krrrunky303
So, the long story short is that I made a 2TB exFAT partition in OS X to share between Windows and OS X (which I've since realized is an awful idea).

It first screwed up a couple days ago when somewhere between being used by OS X and Windows XP the primary boot sector got corrupted, luckily the alternate boot sector was still there and fine so OS X repaired it with fdisk and all was well.

Now I went back and forth from OS X and Windows 7 which seems to have completely annihilated the drive. Before booting into Windows 7, I ran TestDisk in OS X. When I ran it in OS X, I saw a Mac HFS partition at the very beginning, and then it immediately skipped to 50% cylinders analysed and gave me three MS Data partitions. However, TestDisk only seemed able to recover that one Mac HFS partition and listed all the MS Data partitions as unrecoverable, so I left the disk be.

I was worried about stability as I had just installed 10.8, so I booted back into Windows 7 - Windows sees it as two big 1TB RAW partitions and OS X is still unable to repair the drive. OS X still sees it as one 2TB exFAT partition, but is unable to repair it or mount it.

So here are my screenshots of all the steps (don't mind the incomplete statuses of the scan, i've run it up to 100% before a few times and only got this far, was just redoing it for the screenshots):

from a deeper scan

I've been going through tons of threads in the Filesystem Repair and Partition Recovery boards, and I've seen other people with giant lists of Mac HFS partitions like this, but I'm not quite sure what to do with them.

The very first thing I did after zeroing out and formatting that drive as exFAT was to make a disk image of another hard drive which came out to be a little under 500GB. I assume that's at the beginning of my drive and is the data that I care about the most.

Re: Saving a 2TB GPT exFAT filesystem

Posted: 02 Aug 2012, 21:10
by Fiona
Looks like that partitions ends after disk limit.
To figure out the value, you can use a trick.
Easily use partition table type intel.
Please have another try to scan for your partitions.
It's only intended for a diagnose.
But it shows thew values how much you can try to increase your disk size.
Will be similar like in this cases; ... icky#p3951 ... icky#p3435
If your partitions are found, I can determine the amount of cylinders you need.
Afterwards of course, the diagnose will be repeated using EFI GPT but you can increase the amount of cylinder of your disk.
Currently, TestDisk doesn't support a boot sector diagnose and repair of an exFAT-drive.
But can write it to a partition table or GUID partition table.
So hope that your boot sector ist still ok.


Re: Saving a 2TB GPT exFAT filesystem

Posted: 03 Aug 2012, 04:39
by krrrunky303
Thanks for your help Fiona!!

I went through both those threads you linked.
I also did a search to 100% (not deeper search) as Intel, but not feeling confident about the results:


I'll start up a deeper search and let you know if I come up with anything! Thanks again!

Re: Saving a 2TB GPT exFAT filesystem

Posted: 03 Aug 2012, 21:39
by krrrunky303
Okay, so today I manually input the number of cylinders in for a EFI GPT scan, and it shows two overlapping MS Data partitions which judging by the number of cylinders looks like it should be taking up almost the entire drive...


How should I fix the number of sectors so partitions are listed properly?

Re: Saving a 2TB GPT exFAT filesystem

Posted: 31 Aug 2012, 14:47
by cgrenier
Currently there is an HFS partition, this filesystem is supported only by Mac OS X.
The second partition, a very small one, is listed twice because no signature for a filesystem is seen.
TestDisk has seen no exFAT filesystem, so if you have data to recover, you may want to try PhotoRec, note that it won't recover the original filenames...