[CentOS] Re: Installation problem, possibly RAID

Les Mikesell lesmikesell at gmail.com
Sun Sep 11 16:41:16 UTC 2005

On Sun, 2005-09-11 at 05:40, Edward Diener wrote:

> I was doing it so that if I ever needed to move my root partition, while keeping 
> the same partition order, I would not need to reinitialize grub on the boot 
> partition. I was told however that grub does not have the smarts to recognize 
> where its root partition is at run-time so that I would have to reinitialize it 
> anyway if I moved my root partition.

I thought you could specify root=LABEL=xxx in the grub kernel line.  I
usually avoid labels when making custom changes because the stock
labels aren't unique and the system cannot deal with duplicates
if you ever move a disk to a different machine but it should work
if you just shift them around in the same box.  It might be better to
use LVM identifiers which are probably unique if you don't do full
disk image copies to clone machines. 

> In general Linux's reliance on partition order in mounting hard disk partitions, 
> and evidently grub's reliance on specific hardcoded hard disk geometry in order 
> to find its root partition, seem primitive to me.

In the first stages of booting you are at the mercy of the BIOS in
rom.  Lilo pre-computes the disk sectors that will need to be
loaded to the the kernel and initrd into memory and stores the
map in bios terms, so you have to re-run lilo after any change to
lilo.conf.  Grub loads through stages that eventually know enough
about the filesystem to find and read grub.conf at boot time, but
you still have the problem of having to map everything you want
into bios terms and fitting within the bios limitations until the
kernel and initrd are in memory so you have real disk drivers. 

> I could be wrong but I thought 
> that hard disk information on PCs was a pretty well determined thing and a 
> better system would automatically detemine these things at run-time.

It's slightly better than in the years when PC disks had a 32 meg
maximum size, but not much.  Even more recently the 1024 cylinder
limit has been in bios for so long that I just always put a /boot
partition first on the first drive automatically even if it is
not always necessary these days.  

   Les Mikesell
    lesmikesell at gmail.com

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