booting off GPT partitions

John Baldwin jhb at
Thu Jan 28 16:25:57 UTC 2010

On Thursday 28 January 2010 7:26:24 am Dimitry Andric wrote:
> On 2010-01-28 13:06, Robert Noland wrote:
> > John or Marcel can correct me, but I don't think that this is an issue.
> > The bootstrap is located in the pmbr in sector 0 and the GPT headers and
> > tables are in sectors 1 - 34.  The bootstrap code knows how to read the
> > GPT tables and can deal with>  2 tb lba's.
> Ah yes, I see it now.  It uses EDD packets with the BIOS int 13
> interface, which apparently have a 64-bit LBA.  This should support up
> to 8 ZiB with 512-byte sectors...
> OTOH, I have no idea how well most BIOSes actually implement this.
> Since many OSes simply don't support anything over 2^32 sectors, I would
> not be amazed to find much BIOSes out there that behave the same.  Or am
> I too paranoid now? :)

It should work fine.  The GPT boot code was originally written specifically to 
supporting booting from RAID volumes > 2TB.  I've tested it on mfi(4) volumes 
that large (though I didn't verify the individual LBAs of all the various bits 
read in by the bootstrap and loader were).  I know that other folks ran into 
bugs until the ZFS GPT boot code was all made 64-bit clean and that they have 
since booted > 2TB ZFS volumes ok.

John Baldwin

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