Re: Message from grub2-install

[Neal Murphy]

On Saturday 10 March 2012 14:56:57 Stefan Misch wrote:
> Hi Michael,
> 
> So in fact, the MBR stays at 512 Bytes because that's the standard for a
> traditional partitioning system. That is where the actual boot loader
> is. But the core.img-file is indeed placed between the boot loader and
> the first partition. Usually operatings systems begin at Sector 63
> leaving roughly 31k of space available. With the new drives this gets
> pushed back even further to 2048.
> 
> 
> Am 10.03.2012 13:37, schrieb Michael D. Setzer II:
> > On some machines, where I moved the first partition from 63 to
> > 2048 the process runs with no error. In looking at the hex code of
> > the process it seems to be the regular mbr, but then it is followed
> > by the core.img file after that?

There're all manner of weirdities to be found between grub2 and msdos and gpt 
partitioning.

Sector 63 is simply the start of cylinder 1. Works great for old partitioning 
schemes that still use CHS reckoning. Sector 2048 (maybe 1MiB; I don't have a 
new 4kB sector drive to test with) is the place parted uses for the somewhat 
more modern GPT partitioning and modern drives that treat the drive as a 
sequential series of blocks (much like SCSI did 20 years ago). 

For GPT partitioning, IIRC, I had to start the first partition at 1 MiB; it 
was the only way to shut parted up (never mind the contortions I had to go 
through to make it stop silently recomputing partition boundaries on me). Then 
I had to make the firt partition a bare 1-2MiB grub_boot partition to keep 
grub2 happy. This partition contains *no* filesystem; it is merely the place 
where grub lays down its stuff. If you use a /boot partition, that must be 
another partition; fortunately, GPT has 'unlimited' partitions.

I eventually gave up and went back to legacy with RedHat's mongo patch for two 
reasons. First, grub2 picks the wrong drive, ignoring the drive I *tell* it to 
use, or it is unable to find any drive in the first place. Second, I could not 
get it to work on ISO, flash *and* hard drive. I'll re-visit grub2 some time 
after it comes out of beta.