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I just received 4 SATA II Seagate Barracuda 2TB drives that I intend to use for various purposes. Looking at Vista's Disk Management utility I find that all 4 drives come from the factory as GPT disks with the following partitions

[31MB unallocated][2GB primary Partition] [4GB primary Partition] [512MB primary Partition] [1847GB primary Partition] [9.47GB unallocated]

My Vista 64 OS automatically mounts the 4th (and largest - 1847GB) partition, and as I try to access it by double clicking, it brings up the formatting wizard as you'd expect. If I select a full format for this volume, I imagine that in 5 or 6 hours I'll have a 1847GB NTFS volume on a GPT disk.

Now, to say that hardware wasn't my forte would be generous, so I apologise for my naivete in advance, but here are my questions:

Are all these partitions and unallocated space necessary for GPT to function or are they just garbage? If they are necessary for GPT, why are they taking so much space? 16GB seems excessive, no? Is this possibly a Seagate specific hack required to get their Barracuda drives (quite a popular and widely used brand) to work in a specific manner?

Given this drive is not over the 2TB MBR limit I was expecting to be able to convert it to MBR, however the options to convert from GPT to MBR (and vice versa) are greyed out on my Disk Manager (for all disks, not just this one). And yes, I am running it as Admin. Any ideas as to how to convert to MBR? Any warnings, issues I should consider?

I should also note that I have been unable to get Vista Disk Manager to recognise the entire disk as a single volume. Deleting all partitions from Disk Manager still leaves you with two separate unallocated spaces that cannot seem to be convertible into just one. If you try, you get a warning that you are about to convert the disk to a dynamic disk which I don't want to do (certainly not as the end result anyway). It appears that any attempt to create a single volume greater than around 1850GB triggers this warning. Any ideas as to why this is?

All help is greatly appreciated.

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I don't know why Seagate has shipped its drives like this, but my guess is that the three smaller partitions contain Seagate software of some sort. It's possible that one of them is an EFI System Partition (ESP), which is used as part of the boot process on EFI computers. You might learn a little more by looking at the disk with my gdisk program. (A version is available for Windows, or you can use a Linux emergency disk.) Its output will look something like this:

# gdisk /dev/sda
GPT fdisk (gdisk) version 0.8.5

Partition table scan:
  MBR: protective
  BSD: not present
  APM: not present
  GPT: present

Found valid GPT with protective MBR; using GPT.

Command (? for help): p
Disk /dev/sdb: 625142448 sectors, 298.1 GiB
Logical sector size: 512 bytes
Disk identifier (GUID): B58D5E92-7BFB-4488-94B9-2F1BCFDD86DB
Partition table holds up to 128 entries
First usable sector is 34, last usable sector is 625142414
Partitions will be aligned on 2048-sector boundaries
Total free space is 2014 sectors (1007.0 KiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1            2048          514047   250.0 MiB   EF00  EFI System Partition
   2          514048          923647   200.0 MiB   8300  /boot partition
   3          923648       625142414   297.7 GiB   8E00  Linux LVM

This example is of one of my Linux disks. The most important data for your question is under the Code column, which shows gdisk's internal coding for the partition type codes. You can see what the codes are by typing L at the main prompt. Codes you're most likely to see are EF00 (ESP), 0700 (Microsoft filesystem data), 0C01 (Microsoft reserved), and 2700 (Windows Recovery Environment). The codes used on your mystery partitions might provide a clue about what they're for. If the code is FFFF, that means that gdisk doesn't recognize what it is, which in turn means it's probably something Seagate-specific.

In terms of GPT itself, the extra partitions you're seeing are not necessary; a GPT disk with just one partition is perfectly legal. (Even one with no partitions is legal, but pretty useless until you add partitions, of course.) I can't guarantee that Seagate isn't doing something weird with extra software or drivers that might require those partitions, though.

It's possible to convert from GPT to MBR with any number of tools. Windows is supposed to have such a feature, but if it's not working for you, I can't advise on how to fix it. I can say that gdisk has a lossless GPT-to-MBR function:

  1. Launch gdisk on your disk.
  2. Type r to enter the recovery & transformation menu.
  3. Type g to convert from GPT to MBR.
  4. Type p to verify that your partitions are present.
  5. Optionally, type o and enter a number to omit a partition; repeat as often as you like.
  6. Type w to write your changes.
  7. Type Y when asked to finalize and exit.

You might need to reboot before Windows will see the disk using its new partition table.

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I would vote this answer up if I had the rep, as it is indeed helpful. My only concern is it's requirement to download and execute an unknown program. – OldSchool Mar 13 '13 at 11:13
up vote 0 down vote accepted

Ok I have resolved my issues in the following manner.

It appears that

  1. DiskMgmt.msc provides only a subset of the functionality of DiskPart.exe as per and

  2. The junk partitions on my drives were probably OEM hidden locked partitions typically used to store recovery software. Why Seagate had them on drives that were not to be delivered inside a machine I don't know. Perhaps these drives were at some point destined to go inide some OEM machine, not sure.

At any rate DiskMgmt is unable to remove such locked partitions, but DiskPart.exe CAN as per

Once I removed these, I was able to use DiskMgmt as normal to convert the disk to MBR, partition then format the drive as desired

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