Greater than 2TB disks bootable?

[Chris Snook]

Phil Meyer wrote:
> There is a lot of confusion available from articles on the Internet 
> about whether or not a greater than 2TB disk can be made bootable in Linux.
> 
> In order to go that large, the disk must be labelled, via partd, as type 
> GPT.
> 
> Ok so far.

Not really.  x86 BIOSes don't know what to do with GPT-labeled disks.  You need 
an EFI system (rather than BIOS) to boot from a GPT disk.  At the moment that's 
mostly Itanium and certain niche x86 boards.

> Now, is it possible to use fdisk to cut off 100MB or so for a normal 
> /boot partition?
> It seems that labelling a disk as GPT does not stomp the MBR, but does 
> affect the partition table.  Is this correct?

GPT reserves the first sector for a "Legacy MBR", which is basically intended to 
keep legacy disk utilities from doing stupid things to GPT disks.  It isn't 
really used for booting.  EFI uses a FAT partition to hold the bootloader.

> If I create a 100MB partition using fdisk, and then label the disk as 
> GPT, can I start the large partition with the first cylinder > than what 
> I cut off for /boot and expect it to be seen?
> 
> Anaconda complains that GPT is not bootable.  Is that system specific, 
> BIOS specific, anaconda error reading the BIOS, ???

You need a GPT-aware firmware such as EFI for it to be bootable.  If your system 
has a BIOS, it won't work.  The exception is that on some x86 systems, EFI will 
emulate a BIOS for compatibility with OSes that expect a BIOS, so if you can get 
it to actually act like EFI rather than a BIOS, you could make this work.  I'm 
told this is true with some Intel Macs, but I've never played with it myself.

> Here is the specific scenario:
> 
> An intel based server, with 10 1TB drives attached to a SATA RAID 
> device.  The RAID is level 5 with 9 drives and a hot spare.
> 
> What the system sees, is one device of ~8TB.
> 
> Is it possible to boot from the device, AND have all but /boot as one 
> large partition?

Probably not.  You have two choices:

a)	Partition off a small chunk of the array in the RAID firmware.

b)	Add a boot disk.

For a server that does anything important, (a) is probably the safe way to go. 
If I had this problem on a personal system, I'd dig up my old 64 MB USB key and 
choose (b).  I've done it before, and it's just fine for /boot as long as you're 
not hotplugging it or suspending and resuming the system.

-- Chris