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I am in a sticky situation. I recently acquired a 4TB SeaGate HDD, and want to divide it evenly for two Operating System installs. However, my current motherboard only supports MBR/BIOS, and I can't use EFI/UEFI (not supported by my hardware). Therefore, I can't use GPT. I wouldn't be able to boot from it. Furthermore, I am limited to just over half of the HDD's original capacity - 2.2TB. I am not trying to make an OS partition and a data partition. I am trying to dual-boot the system, with each OS being assigned approximately 2TB of storage space. The operating systems I am using are Windows 10 Enterprise and Windows Server 2016. My question:

Is it possible to divide the HDD into 2 'virtual hard drives', by using multiple MBRs on the 4TB hard drive? If it is possible, please explain how or provide a source. Also, Why/Why not?

I want the Operating Systems to see the 4TB HDD as 2, 2TB HDDs. This would possibly allow me to fully allocate the space on the HDD without resorting to GPT (non-bootable). I am okay with using 3rd-party software, but would prefer not having to buy 2 separate hard drives. Furthermore, I cannot resort to using data partitions - that would be equivalent to doing two OS reinstalls, seeing that most of my programs and data are already present on the physical drive. I would possibly have to move/remove everything and start fresh (which took weeks, since drivers are scarce for some of my devices).

If you need a visual for reference, here are some screenshots:

1 Answers1

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Multiple MBRs: No.

But there might be a couple other ways to use most or all of your 4 TB HDD with a motherboard with a BIOS.

Back up your data before trying either of these!

  1. Look into using 4096-bit sectors (also known as Advanced Format), instead of 512-bit sectors. This allows partitions up to 16 TiB. Since Windows 10 and Windows Server 2016 are both quite a bit newer than Windows XP, they should support the larger sectors. You may need to check compatibility with your HDD, partition tools, and BIOS, however.

  2. Make the first partition slightly less than 2 TiB, then place the second partition just before the 2 TiB mark. MBR partitions consist of a 32-bit pointer to the start of the partition, plus a 32-bit length. Although most addresses in the second partition will require more than 32-bits to represent, that doesn't matter to the MBR. It does, however, matter to the boot loader and the operating system. According to this 2011 article, such a scheme works with Windows 7, so it may also work with your OSs.

  3. You might actually be able to boot a GPT disk with your BIOS anyway, by using a bootloader that does support GPT. The general idea is to set the boot flag in the protective MBR, then use the BIOS to boot a bootloader, such as GRUB, which would then read the GPT and allow you to boot into your actually operating systems.

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8bittree
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  • I find the first option quite interesting. Advanced Format (4096B sectors) appears to be a feature on my HDD: https://drive.google.com/open?id=0B98YR-Jm_dNAelBMZVRIZHE2R0U –  Oct 05 '17 at 22:22
  • Advanced Format feature checked using the link below: https://support.symantec.com/en_US/article.TECH194586.html I have the Gigabyte GA-EP45-UD3P. I'll need to check BIOS compatibility next... –  Oct 05 '17 at 22:27
  • As I understand it, most HDDs these days do use 4096 bit *physical* sectors, but **some** present 512 bit *logical* sectors for backwards compatibility. The trick would be to make it present the full 4096 bit size and to make sure all your software is happy with it. That said it's also been several years and operating systems since AF drives were introduced, so it might be more straightforward these days. – 8bittree Oct 05 '17 at 22:29
  • In the image I sent, I saw the following details that appear to confirm your data: /.../ Bytes Per Sector : 512 Bytes Per Physical Sector : 4096 /.../ If such is the case, how would I go about changing this? –  Oct 05 '17 at 22:33
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    I'm not sure. It seems like it might require an adjustment to the HDD's firmware (and would almost certainly require a reformat, so **backups!**). Would probably make for a good additional question. – 8bittree Oct 05 '17 at 22:45
  • I was unable to find a firmware update for my HDD from SeaGate. Quite sad really - I guess I'll have to look into GRUB? –  Oct 05 '17 at 23:10
  • I also found this a few minutes ago: https://sourceforge.net/projects/grub2win/ It appears to be a GRUB2 distro of some sort. Would this be capable of booting Windows from GPT? If so, I would have BIOS boot GRUB2 first, then have GRUB2 boot Windows from GPT partitioning scheme. –  Oct 05 '17 at 23:33