Mark Lloyd wrote:


BTW, "over 2TB" (requiring GPT) applies to the physical drive. MBR won't
allow you to use more than 2TB, regardless of partition size (this is
because of MBR using 32-bit fields for sector number). ( 2 ^ 32 ) * 512B
= 2TB.

Actually, there is a way to do that. And the software is part of
the free version of Acronis TIH on the Seagate and WD sites.

The idea is, when a drive is over 2TB, a filter driver is installed
by Acronis, which takes sector offsets above 2TB and makes them
into a virtual drive. The second virtual drive then shows up in
Windows. So perhaps in Disk Management, I'd see "Disk 3 2048GB" and
"Disk 5 748GB". If you examine the physical disk, there is a
second MBR at roughly 2TB plus 256KB or so. So it's like two
MBR-limited disks, living on the same storage device.

The Acronis "Extended Capacity Manager" is the thing that installs
the driver and makes it work.

Once you've done that, you can boot Linux, and do a loopback mount
of the area above 2TB. You have to work out the offset precisely,
and the Linux mounter accepts an offset above 2TB (64 bit offset).
The only problem, when I tested that, is it's dreadfully slow.
The NTFS partition mounted that way, could only copy files at
10MB/sec.

The Acronis TIH solution does work, but it's a bear to get it
running. Most of the time, the option to use Extended Capacity
Manager will be grayed out and it won't work. I had to do a
lot of fiddling with it, until it worked. At least Acronis
have now figured out how to remove that filter driver,
as in previous versions of TIH, they could install but not
remove the filter driver. The claim was, at the time, if
you attempted to remove it manually, it would blue screen the
computer. But now, you can even get the filter driver as
a separate package. I installed just the filter driver
in Windows 8.1 Preview, and my 3TB drive could be "seen as
two drives" in Windows 8.1. So I was able to test that
the scheme could work in a couple OSes. But it's not
an experience I'd look forward to again, trying to get
it to work on a new disk drive.

*******

That doesn't change the fact, as you point out, that the MBR
is limited to 32 bit sector addresses. That limit is still
present, but the filter driver idea at least allows the
capacity to be used, by preparing a virtual drive to use
the rest of the capacity.

One RAID controller (Areca) solves this problem, by abusing
the notion of sector size. If your array size is larger than
2TB, you can tick an option to pretend sectors are 4KB in
size, and then a larger array can continue to use MBR
instead of GPT. (i.e. 32 bit sector address times 4KB,
to give addressing up to 16TB or so.)

*******

As for an OS defaulting to GPT, that might have something
to do with UEFI support in the BIOS or something. My experience
here, loading a modern OS on a legacy BIOS motherboard, is it
defaults to MBR. It could be, that GPT is preferred, if
the Disk Management recognizes that GPT can be made to
work for booting the OS.

Paul