Why can I only use half of my huge 4TB external Seagate hard disk drive with Windows XP, Vista and Windows 7 and 8.1?

PROBLEM: I have a 4TB Seagate external hard drive but only half of the drive is available for use and I wasn’t able to make Windows 7 create a system image or backup on it. Seagate support advised me to download their DiscWizard tool in order to be able to use the whole drive. Is that correct or is there a better way of solving this problem? Also, if and when I can make backups, how much disk space will be required for a full system-image backup? The computer is using 220GB of its 500GB internal hard drive. I want to save system images and backups of four computers – two desktops and two laptops – on the drive, so I need to know the best way of not mixing them up. In the event of an irrecoverable problem on one of them, I don’t want to restore the wrong system image to a computer.

ANSWER: Most computers still use the Master Boot Record (MBR) format employed by the NTFS file system, which most internal and external hard drives are formatted to use. MBR formatting is not possible on drives, or partitions within drives, larger than 2.19TB, therefore, since your PC uses MBR formatting, only half of the drive can be formatted and a drive has to be formatted to use a file system before it can be used. If you want to format your 4TB drive using MBR, you’ll have to make Windows split it into two 2TB partitions in Disk Management and then format them by using Disk Management or by right-clicking on each of the partitions under Start => Computer in Win7. After formatting, a drive, Windows assigns it a drive letter.

Of course, with drives that have storage capacities larger than 2.19TB there would have to be a file system able to format without having to partition them.

The GPT file system can format any current size of drive and will be able to do so for many years to come.

Windows Vista, Windows 7 and Windows 8 fully support drives larger than 2.19TB. For example, Windows Disk Management can format a 3TB external drive normally as long as the user chooses to format the drive as a GPT partition, which allows Windows Vista/Win7/Win8 to create a single partition of a drive with a capacity exceeding 2.19TB. GPT uses 64-bit addressing that allows a truly enormous partition size of 10 zettabytes (ZB) – a 1 followed by 21 zeros, measured in bytes of information. The number of bytes of information in a terabyte (1TB) is a 1 followed by 12 zeros. Every time a zero is added the whole number is multiplied by ten, so the GPT file system is going to around for a very long time.

GUID Partition Table [GPT] – http://en.wikipedia.org/wiki/GUID_Partition_Table

Using GPT Drives –


The Master Boot Record (MBR) format used by the FAT followed by the NTFS file systems, used for decades, has a maximum partition size of 2.19TB, therefore for partitions larger that they have to be partitioned as GPT partitions. It’s to do with a 32-bit limit that goes along with the RAM-memory limitation in 32-bit systems of 3.2GB. To use bigger partitions requires 64-bit addressing and more memory requires using a 64-bit version or Windows (Vista, Win7, Win8) or another 64-bit operating system, such as Linux.

The new GPT format also allows you create more than four primary partitions on the same drive. MBR can only be used to create four primary partitions (defined as a partition that can be used as a bootable system partition). A primary partition can be further partitioned into one extended partition that can itself be partitioned into logical partitions that are each given a drive letter (G:, H:, etc.) but can only be used for data storage or have software installed on them that is not the operating system. A bootable operating system has to be installed on a primary partition.

On PCs, full GPT support requires a 64-bit version of Windows (Vista/Win7/Win8) and a UEFI (Universal Extensible Firmware Interface) BIOS. Note that from Vista to Windows 8, 32-bit and 64-bit versions are available. A 32-bit version of Windows cannot be upgraded to a 64-bit version. To have a 64-bit version requires a clean installation using the 64-bit installation DVD for that version.

Systems that have a standard BIOS and/or a 32-bit version of Windows installed can be made to work with partitions larger than 2.19TB by employing intermediary software, such as Seagate’s DiscWizard, that takes care of the addressing conversions.

Seagate DiscWizard tool: A site with a free download, user guides, and more –


To open Disk Management, which provides the information and formatting options on the installed data-storage drives, enter the diskmgmt.msc command in the Start => Search box in Vista/Windows 7 (it’s the Run box in XP). In Windows 8, press the Windows key (the one with a flag on it) plus the X key on the Desktop screen to bring up a menu containing it, or press the Windows key (the one with a flag on it) plus the R key to bring up the Run box and enter that command in it.

Windows XP cannot format drives exceeding 2.19TB, but if the drive is an external, non-boot drive, the drive manufacturer can provide an installation option to format it for Windows XP compatibility. The external drive’s user manual should explain what to do.

This article reviews four 3TB hard drives made by Hitachi, Seagate and Western Digital, providing information on why they don’t always work as expected:


With regard to the size of backups compared to the original amount of data on a drive, backups and system images are compressed to a certain extent, so will be a little smaller than the original amount of disk space occupied by the data. Data files can be compressed by about 30%, but most image and sound files are already compressed and can only be further compressed by a few percent. Empty space is compressed 100%. Therefore, the size of a system image or backup depends on the mix of file types the original data contained. 220GB of used drive space created into a system image would probably require somewhere between 180 and 200GB of external drive space.

With regard to restoring the the wrong backup set, the best way to avoid doing so is to create separate backup folders for each computer. Give each computer a recognisable name (Mary’s laptop, Office desktop, etc.) and then create a folder with the same name on the external drive for that computer. Then you just have to make sure that the backup or system image is created in the correct folder. If you have to perform a restoration, then it’s just a matter of navigating the restore process to the correct folder.

After Windows can see and access all of your external drive, you should be able to create backups and system images without any problem. just remember that a backup allows individual files and folders to be restored and that a system image can only be restored as a whole.

The following article provides detailed information on the 2.19TB barrier.

The 2.19TB Barrier –


[Almost] Everything You Need to Know About 3TB Hard Drives –


About Eric 275 Articles
I am an experienced PC technician who has been the owner and sole writer of the PC Buyer Beware! website since 2004. I am learning all the time in this very dynamic, ever-changing field.