BIOS booting from disks > 2TB

Borja Marcos borjam at
Mon Nov 17 12:05:59 UTC 2014


I've been trying to install FreeBSD on a 3TB disk attached to a Proliant Microserver G8.  The system
is unable to boot, complaining about an error with the GPT backup table. I don't have the machine here now,
but I can reproduce this evening if someone really needs to see the actual messages.

The machine doesn't have UEFI, it can just boot via BIOS, and I understand that the reading of the backup table is
failing because the BIOS can just use 32 bits to specify a sector number.

Would it be possible to "fix" the boot process so that, if the following conditions apply, that check is omitted?

- Boot using BIOS, not UEFI

- bits(disk size) > 32

What would be the side effects? Of course we can't assume it will be safe to boot from a ZFS pool with
devices larger than 2TB, as there is no guarantee that all the blocks it needs to read are  within the 2 TB limit. 
But it should be safe to, at least, boot from a UFS partition contained below the 2 TB limit.

Any thoughts?


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