Booting from 3TB drive (UFS, BIOS)

[Oliver Fromme]

John Baldwin wrote:
 > On Tuesday, August 14, 2012 9:23:19 am Oliver Fromme wrote:
 > > I've got a small PC that currently has two disks:  The
 > > first one is 1 TB with a standard MBR, used to boot FreeBSD,
 > > and the second one is 3 TB with GPT, used as data disk for
 > > FreeBSD (the BIOS doesn't have to care about this one at all
 > > because it's not used for booting).
 > > 
 > > Now I would like to replace the first disk with a 3 TB one,
 > > too.  However, will I be able to boot from it?  The PC is
 > > not exactly a new one (ASRock A330GC with Atom 330 processor,
 > > a few years old) and has a standard BIOS (dated 07/16/2009).
 > > 
 > > I understand that I will have to use GPT in order to be able
 > > to use the full capacity of 3 TB, and that I will have to
 > > install a pmbr to enable the BIOS to detect the disk as
 > > bootable.  Is this correct?  Will that work?  (Assuming that
 > > the boot partition will have to be within the first 2 TB of
 > > the drive, of course.)
 > 
 > A GPT boot should work, and the boot partition can even be
 > above 2 TB.  (GPT booting only uses the EDD BIOS interface
 > which uses 64-bit LBAs, and the GPT boot code will use all
 > 64-bits of the LBAs stored in GPT, etc.)

(I'm sorry for the late reply; I still haven't gotten around
to upgrade the disks ...)

Problem is, the machine doesn't have an EFI BIOS and does
*not* support GPT.  So it will use the compatibility MBR
of the GPT, I assume.  And MBR isn't able to represent
addresses beyond 2 TB, so the slice containing the boot
partition will have to be within the first 2 TB of the
drive, right?

I tried to research the issue, but Google mostly returns
pages concerning Linux that advise to use disks > 2 TB as
data disks only while using a separate disk <= 2 TB for
booting, unless you have an EFI BIOS that supports GPT
natively.

Best regards
   Oliver


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