I installed a new/larger (4TB) hard drive on my computer. I have Windows 7 installed on the old drive (1TB) and using backup of the drive with a system image, I restored that to the new drive. All seems to work fine.

Now I want to extend the partition on the new drive. In Disk Management, I can see the unallocated disk space next to the allocated C: drive. There are no logical partitions, just the allocated and unallocated sections. When I right click to extend the C: drive, the "Extend" option is disabled.

partition list

Why would it be disabled and is there a way for me to enable it?


I found some posts that says it has to be converted to be a dynamic disk first, but this option is also disabled.

  • Can you provide a screenshot? Is the unallocated section right next to the partition you want to extend, or is there another partition in between? Windows can't natively move partitions so can only extend to adjacent unallocated space. Side note, dynamic disk is not at all required and is definitely not what you want here. – Bob Jan 8 '18 at 4:17
  • It should have been converted to GPT which is different and unrelated to "dynamic disks", a Windows only feature. That is due to the size of the drive. – user772515 Jan 8 '18 at 4:19
  • Screenshot added. After a quick read on GPT, it looks like converting it requires deleting the current C: partition. :( – sdoca Jan 8 '18 at 4:28
  • This: blogs.technet.microsoft.com/askcore/2010/02/18/… and unfortunately, unlike Linux, Windows requires MBR ("msdos") for BIOS installs and GPT (GUID) for UEFI installs. With this in mind, the cloning you did may work (boot) but certainly it won't allow extending the partition. If the PC is UEFI I suggest reinstalling in UEFI mode to the new drive (USB stick required, Win7 DVDs can't install in UEFI mode). – user772515 Jan 8 '18 at 4:39
  • Thanks, looks like I have some reading to do on how to install in UEFI mode. – sdoca Jan 8 '18 at 4:57

2TB is the maximum partition size of any MBR format disk.

Understanding the 2 TB Limit in Windows Storage

Windows 10 Creators Update provides us a safe, and non-destructive method of converting MBR to GPT using MBR2GPT.EXE. Unfortunately, you don't have Windows 10.

The safest alternative is to just create a secondary partition to use the remaining space. The new partition will show up as a new drive on your computer, and you can save data to it.

Only Windows 7 64-bit running on UEFI hardware supports booting from a GPT partitioned disk drive. If you're running on older hardware, or 32-bit, you are SOL. If your system meets these requirements and you are adventurous, the drive can be converted from MBR to GPT. The official way involves backing up your data and deleting all partitions to create a new GPT layout and then restore data. But, there are ways to convert MBR to GPT without losing data.

WARNING: Always verify you have a good backup of data BEFORE attempting to convert MBR to GPT.

Here are a couple of options:

In my opinion, you really should not be trying this. It is likely to fail. If you need a partition size greater than 2TB, is it unreasonable to expect you to also have a modern operating system, on modern hardware?

  • 1
    +1 except for the last sentence. Windows 7 is still supported by Microsoft and while not the latest version, it's still too widely used to be considered non-modern IMHO. – Twisty Impersonator Jan 8 '18 at 13:16

The common response to this is that MBR doesn't support drives larger than 2TB, like mentioned in the other answer

That's true but not entirely correct. The real technical limit is 232 - 1 sectors, since MBR uses 32-bit index to address the sectors. Therefore on old drives with 512-byte sector you'll be maxed at 232×512 = 2TB and for new drives using Advanced Format (AF, i.e. 4KB sector) you can have 16TB MBR drives!

I'm not sure if diskmgmt.msc can create big partitions on AF drives or not since it has many artificial hardcoded limits and falls pretty far behind on features as well as capabilities compared to 3rd party disk partitioners. You need to check if your disk format is AF and if it really is you can use a 3rd party solution to resize your drive

If it's not, don't fret yet. You can go even higher, up to nearly twice the above limit and have a multi-partition 4TB MBR disk as long as the last partition begins before the 2TB mark and doesn't last longer than 2TB. The technical explanation behind that is

MBR records partition locations in terms of the starting sector and the partition's length. Both of these are 32-bit values, so in theory you could use MBR on a 4 TiB disk, so long as all the space after the 2 TiB mark is in a single primary partition, or perhaps in a single extended partition, which could in turn hold many logical partitions. Such a configuration would be somewhat limiting, but it fits within the MBR framework

Working Around MBR's Limitations

Of course you need OS support for this, and also need a 3rd party disk partitioner instead of diskmgmt.msc. However Windows 7 and above do support those disks well, thus there should be no problem. To quote from Rod Smith's article above

To make a long story short, the only OSes that seemed capable of handling a partition that spanned the 2 TiB mark were Linux, FreeBSD, and Windows 7

In your case you just need to shrink the C: drive a tiny bit to make it smaller than 2048GB and create another partition on the remaining 1678GB space. Note that you can't have a single huge volume in this case, but at least you can use the whole drive

Since partitioning information is stored in the MBR partition table using a beginning block address and a length, it may in theory be possible to define partitions in such a way that the allocated space for a disk with 512-byte sectors gives a total size approaching 4 TiB, if all but one partition are located below the 2 TiB limit and the last one is assigned as starting at or close to block 232−1 and specify the size as up to 232−1, thereby defining a partition that requires 33 rather than 32 bits for the sector address to be accessed. However, in practice, only certain LBA-48-enabled operating systems, including GNU/Linux, FreeBSD and Windows 7[20] that use 64-bit sector addresses internally actually support this


Note that dynamic disks are completely different and irrelevant to the problem. They're the analog of LVM on Linux for things like software RAID, striping, spanning, online resizing...

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