GPT and MBR

I've run into an interesting problem with the new backup machine.

It's a Sun X4240 with 10 x 15k disks in it: 2 x 73GB (mirrored for the OS) and 8 x, um, a bunch (250GB?), RAID0 for Bacula spooling. (I want fast disk access, so RAID0 it is.) RAID is taken care of by an onboard RAID card, so these look like regular disks to Linux.

Now the spool disk works out to about 2.2TB or so — which is big enough to make baby fdisk cry:

WARNING: The size of this disk is 2.4 TB (2391994793984 bytes).
DOS partition table format can not be used on drives for volumes
larger than 2.2 TB (2199023255040 bytes). Use parted(1) and GUID
partition table format (GPT).

Well, okay, haven't used parted before but that's no reason to hold back. I follow directions and eventually figure out that mkpart gpt ext3 0 2392G will do what I want. GPT? Piece of cake! And then I rebooted, and I couldn't boot up again. Blank screen after the POST. Crap!

The first time this happened, the reboot also coincided with some additional problems during the POST where too many cards were trying to shove their ROM into the BIOS memory (or some such); I thought the two were connected. But then I did it again today, and I finally started digging.

The problem is that parted overwrites the MBR when setting up a GPT disklabel. This has been noted and argued over. My understanding of the two sides of the debate is:

• the MBR is not part of the EFI standard, so it's entirely rational that it should be erased;
• but very few x86 machines are EFI-only;
• and traditional disklabels don't support partitions over 2TB, so what's a brother gonna do?;
• and an MBR-GPT hybrid seems a nice way out of this.

Meanwhile, the parted camp has a number of bugs dealing with this very issue, two opened a year ago, and none have any response in them.

This enterprising soul submitted a patch back in December 2008, which appears to have fallen to the floor.

As for me, I was able to convince the BIOS to boot from the smaller disk, and then get a rescue CentOS image going via PXE booting, and then reinstall grub on the smaller disk. Sorted. All I had to do was change root (hd1,0) to `root (hd0,0) in grub.conf.

A touch anti-climactic after all that, perhaps. But it was interesting a) to learn about all this (I hadn't really thought about successors to the DOS partition format before), and b) to see what a slender thread we (okay, I) hang our hopes on sometimes. It's a necessary, sobering thing to realize how much of what I use, depend on, believe in is created by volunteers who are smart, hard-working people — they argue and and focus and forget just like real people, not inhabitants of some shining city on a hill I sometimes take them for ("Next beer in Jerusalem!").