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Some manufacturers of external hard drives with capacity exceeding MBR partition capacity seem to sell them pre-partitioned to a 2TiB partition and one with the remaining capacity.

Tools are available to make a single, larger partition out of these (at least I think I learned as much from amazon reviews of such products; presumably the disk is in GPT mode afterwards).

Can I go the other way, i.e. use the full space of a 3TB drive, while at least one partition can be used in MBR mode (for booting Windows in a non-UEFI machine)?

The drive is a 3.5" HD Seagate Barracuda something currently inside a USB 3 box. This Seagate Disk Wizard (pdf) for Windows, which may not be helpful anyway, refuses to install for alleged lack of a Seagate HD. I have a (non-UEFI) PC (with SATA I only) available and would not be afraid to use linux-based tools.

  • I don’t think Windows would be very happy with booting from a hybrid MBR/GPT drive. I haven’t actually tested it, though. – Daniel B May 24 '14 at 12:40
  • If I understood some not terribly well-sourced article correctly, the original trick had something to do with making the second partition appear as a virtual hard drive on its own, so no GPT required. – arne.b May 24 '14 at 12:45
  • What are you attempting to do once the drive is partitioned. Perhaps we can recommend a simpler alternative... – Kinnectus May 24 '14 at 12:46
  • That functionality depends on the external disk’s USB-SATA bridge controller. If you plan to install Windows on it, you would need to install it internally. The splitting functionality won’t work in that case. – Daniel B May 24 '14 at 12:46
  • @BigChris Use it as a drive for Windows and other stuff. Put backup image of old hard disk somewhere at the far end of the disk. An obvious simpler alternative would be to live with a 2TiB disk until an UEFI PC comes around, but I wondered if I could do better. – arne.b May 24 '14 at 12:54
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MBR or GPT is the whole disk's format, not a partition, so you cannot have an MBR partition on a GPT disk. Hybrid MBR/GPT is a drive with both GPT entries and normal MBR entries, not MBR partition on GPT disk.

Some manufacturers worked around the problem by partitioning the first 2TB as MBR then install Windows normally. After finished installing they install a special driver to make the OS recognize the remaining space as another separate drive so you can utilize all of the available space. This may be fragile and not portable so I don't recommend using it this way.

You can boot from GPT disks in BIOS mode with a software UEFI implementation like DUET or Clover, although it's not very easy and will boot a lot slower

Another solution is installing windows on VHD on a GPT disk. Just format the drive as GPT then when installing Windows, press Shift+F10 and create a VHD, mount it and then continue as normal. I haven't tried it but many people have confirmed that it works

You can also partition a MBR disk up to nearly 4TiB by having a single last partition start before the 2TiB mark. For example a 1.99TiB volume and a 750GiB volume, or two 1.5GB volumes

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

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

https://en.wikipedia.org/wiki/Master_boot_record#Partition_table_entries

You'll need OS support for this, and also need a 3rd party disk partitioner instead of diskmgmt.msc. Windows 7 and above will work with those disk without 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

For more information read

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