Why is the "Extend Partition" option disabled?

Solution 1:

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:

• Use EaseUS Partition Master Free
• Use GPTGen

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?