Saturday, January 31, 2015

The 3TB problem, or: where did my drive go?


Have you got a large hard drive (3 TB or more) that shows up as a much smaller one when you go to use it? Read on for a free solution that works under Windows 7 and likely many other 64-bit operating systems.

The problem

Older 32-bit operating systems (like Windows XP) can access 232 different "logical blocks" on a hard drive, each one of which typically has a sector size of 512 bytes. Doing the math 1 gets us 2.2 TB 2. That's the maximum size the MBR (Master Boot Record) supports. So there's no point installing a 3TB hard drive. One-third of it will be inaccessible and wasted.

How do we get around this? One solution would be to increase the sector size. Some disk manufacturers indeed implemented proprietary schemes along this line. But these ran into compatibility issues with certain legacy software. The operating system required special settings. Hack piled upon hack.

A better solution was devised, one that uses a 64-bit partition table. The newer GPT (GUID Partition Table) provides support for 264 logical address blocks. That's 9,444,000,000 TB or 9.4 EB.

EB stands for exabyte, which is a short way of saying "lots of stuff".

Recently I bought a couple of 3 TB drives, but when I put them in my external drive reader, they showed up as a fraction of their size. Attempts to repartition with Windows 7 (64-bit Professional Edition) were fruitless. It's as though the OS was only recognising the old MBR and not the new GPT.

Now, this doesn't make sense, since Windows 7 understands GPT just fine. But I was making no progress until I discovered...

The solution

The free and fool-proof solution is to use GParted, a graphical programme for managing disk partitions. It runs on GNU/Linux distributions, but there is an easy way for Windows and OS X users to access it, using GParted Live. This is a self-contained bootable Linux image that contains GParted and little else.

Here's the step-by-step process. If you need details on any point, refer to the manuals and online help for the specific products. I cannot act as tech support. Disclaimer: Do this at your own risk.

1. Download GParted Live and burn this to either a CD or USB stick, whatever is easiest for you to boot from.

2. Make sure your BIOS has the correct boot order set. You will want it to first check the CD drive (or USB) before it looks to the hard disk.

3. Insert Gparted CD into your drive (or attach the USB stick) and reboot your computer.

4. You will soon see a graphical boot menu. Choose "GParted Live" (the first, default option) and answer the next couple of prompts during boot-up (tap Enter for defaults).

5. When the desktop loads, the GParted application will open automatically. Otherwise, you can run it from the desktop manually (double-click the icon).

6. GParted has a familiar graphical interface. Most things can be done several ways: from the main menu, toolbar or mouse context menu. The first thing you will want to do is choose the correct hard drive using the menu "Gparted > Devices".

7. If you are having trouble knowing which device is your new drive, the best thing to do is to first boot without the disk attached. Make a note of all devices. Then, reboot with the new drive. You can then easily compare the lists and spot your new drive. In my case it was easy to see the 2.73 TiB drive, since it is the largest on my system 3.

8. You can now examine the bar diagram of the partitions on this disk. Depending on its providence, the drive may be completely or partially unpartitioned. Sections that are not ready for use by your OS will be grey in colour and labelled "unpartitioned". Sometimes there might be a special small partition that shows up as "unknown". This may be something the disk manufacturer placed there, so it is best to not tamper with it.

9. Use the menu "Device > Create Partition Tale". For the partition table type choose "gpt" (the default). After a short while you will be back at the main interface. The partition will still be grey, but now says "unallocated".

10. Create a new primary partition. You can have this partition fill the entire disk, or the portion you wish. It is here that you must specify the file system. For Windows you will likely want to use NTFS.

11. Continue adding partitions, extending existing partitions, etc., until you get the structure you want. All of these operations are put into a queue, ready for action.

12. Hit "apply" to perform all of the pending actions in the queue. It takes only a few moments.

13. You are now finished with Gparted. Double-click the desktop "exit" icon. Pause when the dialogue window come up. This is a good time to remove the CD or disconnect the USB stick. Choose "reboot".

14. This time, boot to Windows as you usually would. Run the Disk Management Tool. The easiest way to find this is to simply search for "disk management" from the Windows menu.

15. If all is well, your drive will display with the partitions as expected. You may now right-click a partition to format it. There are also options to rename the partition and re-assign drive letters. I do both because I prefer to keep my drives organised, with an understandable nomenclature.

That's it; you're done. The drive is ready for use at full capacity.

If this saved you time and frustration, consider donating using the Paypal link in the sidebar. Thanks for reading!


1 512 x 232 / 1012 = 2.2

2 Following the protocol of hard drive manufacturers, I will correctly use decimal units in this article. Hence one MB is 1000 KB, one GB is 1000 MB, and one TB is 1000 GB. It is easy to confuse this with binary units, where capacity is calculated in powers of 2. Here each unit is 1024 greater than the next. These units should properly be labelled TiB or tebibyte, but few do this. Microsoft measures disks in binary but incorrectly calls them TB. OSX used to have the same nomenclature problem, but Apple fixed it.

3 Don't be confused that this is not showing up as closer to 3TB. Besides the different nomenclature noted in a previous footnote, all drives have overhead space that is not accessible to users. Drives are always smaller in reality than on the label!


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