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I recently bought a 3TB hard drive (TOSHIBA DT01ACA300). At the time I was prone to using Windows XP because of some old legacy software, so I could only partition a 750 GB part. Now, with Windows 8, the same partition is recognized as RAW and therefore I can't access it.

How do I recover the partition? I'm already using about 500 GB of space so backuping is the least I would like to do (I still have XP on my machine in case of disaster). I already tried EaseUS Restorer but it didn't had the HDD in its database. Right now I'm running testdisk but astonishingly it only found a 2 tiny FAT16 partitions.

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Why are you saying that you could only partition 750Gb? There is no reason why you shouldn't be able to have 3TB hard drive partitioned under WinXP. I think it is high possiblity that you have bought a faulty hard drive. Can you confirm that you can still access it via WinXP? – phoops Apr 27 '14 at 20:08
As far as I know XP has a size limit. And yes, the partition works perfectly under WinXP. – Kimmel Gábor Apr 27 '14 at 20:14
Do you see your other 2250GB in WinXP's Disk Management? (press Win+R -> write diskmgmt.msc -> hit enter) – Jet Apr 27 '14 at 20:25
1 Windows XP only supports MBR which is limited to 2TB. – Hennes Apr 27 '14 at 20:40
up vote 1 down vote accepted

I could only partition a 750GB part.

Lets stop here because this is where your problem starts. The actual drive is probably not 3TiB but 'marketing 3TB'. That is about the same as 2TiB+750GiB.

Your old OS looked at the drive and had a wraparound. Think of that as having two boxes to write numbers in and then you count to 120. It would start like this:

1     (first number)
2     (second)
98    (98)
99    (98)
00    (100)
01    (101)
20    (120).

Rather than wrapping at 100 your OS wrapped at 2TiB. It has a wrong idea about the drive.

"Good enough" tought I, "I can partition the rest later with Windows 8". Turns out Win8 sees the partition as a RAW partition and cannot access it.

Windows 8 (or any OS not limited to MBR) will see the drive as it actual is. It has the right picture which sadly differs from what your XP installation thinks of the drive.

Question is, how do I recover the partition? I'm already using about 500GB of space so backuping is the least I would like to do.

Backupping and repartitioning is exactly what I would do.

Whatever you decide to do, make sure you have a backup first. And test that backup.

Even if it is just in case you break anything while trying to find a different solution. But if you already have a working backup then the quickest way is wipe the disk (start, run, diskpart and then clean ON THE RIGHT DRIVE) and then to repartition it.

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Could you explain or maybe give a link for the 'marketing 3TB' stuff? It seems at first glance odd why wouldn't a single disk be built with 3 TB at the start. – Doktoro Reichard Apr 27 '14 at 20:43
It is an it is not. For most of us computer users computers count in powers of two. One kilobyte be 1024 bytes. One megabyte would be 1048576 bytes. One GB would be 1024x1024x1024. etc. etc. Slowly these 'computer numbers' and the regular SI numbers get more and more different. Marketing always used to biggest number. And with big harddrive you run into this. See for a longer (and possibly better) explanation. – Hennes Apr 27 '14 at 20:46
Ok then, I believe I just misunderstood the paragraph, as I was aware that HD manufacturers have been using a power of ten approach for measuring their HD's capacity. – Doktoro Reichard Apr 27 '14 at 20:52
I did backup and wipe the disk. Turns out I have an ancient motherboard without UEFI, so I'm still back at the 2TB limit, and I cannot format the remaining 750GB (altough Win8 detects the free space correctly). – Kimmel Gábor Apr 28 '14 at 17:57

MBR (Master Boot Record), and the only partition table Windows XP can handle, does not support drives bigger than 2 TB, according to this Microsoft post.

GPT (GUID Partition Table) is needed to access drives larger than 2 TB and it is available on versions of Windows later than XP. I'm assuming that your drivers on the XP machine let you use some hack using MBR since you didn't use 2 TB or more of the drive. Since the drive is still that large, Windows 8 likely sees that data as above the 2 TB mark, so it can't see it using MBR.

As for getting the data into Windows 8, my advice is that you would be best off getting another drive, so that you can back up and repartition the original drive under Windows 8. You could even buy an external 1 TB drive, copy the data, wipe the drive, then sell it on eBay or something. But you're not going to be able to get the data from Windows 8.

For some more info, look at this link: The gist of it is that, if your BIOS does not support UEFI, you cannot use more than 2 TB of any drive. Even if using a version of Windows that supports GPT, you can possibly use the 3 TB as a data drive, but never as a boot drive. You may be able to partition it into multiple partitions of less than 2 TB, but it doesn't look intuitive or easy.

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I wiped the disk and still cannot format more than 2TB, also my motherboard does not have UEFI. So I guess Win8 still uses MBR. – Kimmel Gábor Apr 28 '14 at 17:59
I added some more info above. – Joshua Nurczyk Apr 28 '14 at 18:03

Windows 8 is probably looking at this as a GPT drive, not as the MBR type drive that windows XP created the partition. At this point, probably best to backup the files for your windows Xperia machine and re-init the drive under windows 8 as GPT.

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