[ILUG] harddisk swap

[Paul Jakma]

On Fri, 30 Apr 2004, Enda wrote:

> The geometries in my experience don't really matter, as long as
> with lilo, its referencing files that reside within some short
> distance from the start of the disk. Lilo doesn't store "offset"
> values to find the files, its uses drive / partition paths.

That would be grub actually. And even grub uses an offset to allow 
the stage-1 loader (on the MBR) to locate the stage-1.5 fs specific 
loader. Only the final stage 2 loader has full drive/path support.

I'm guessing that, just like lilo and the kernel image, you can not
move your grub stage-1.5 file without updating your MBR.

Also, the geometry does matter, well it used to anyway, BIOS disk
addressing interfaces were specified by C/H/S. Different disks could
easily have different geometries, even though they might have the
same number of blocks. This was particularly the case during that
period of time where several different translation schemes were in
common usage for PCs. Even worse, IIRC, for SCSI disks, which,
natively, are block-addressed (as is sane), hence it was down SCSI
controller ROMs to go pick some suitable scheme. The same disk (or
set of disks for RAID controllers) might not boot in the same machine
with a different controller (or even a newer version of the same
controller).

Thankfully, some sanity was brought to the PC world with LBA, which,
though I know nothing about it, presumably is a sane
block-addressable BIOS disk interface if the acronym is to be
believed.  However, as a mark of respect to the short sightedness of
the good old days, LBA was deliberately specified to not be able to
fully address the ever growing sizes of disks for more than a decade
(if even that), topping out at somewhere just above 100GB (130 or
140GB). Hence the introduction of yet another PC BIOS disk addressing
mechanism/interface, LBA48, which should be good into the petabytes
which obviously PC disks will _never_ reach in our lifetimes, never
mind the next decade.

> Drive paths are different. /dev/hda -v- /dev/sda -v-
> multi(0)disk(0)whatever(0)whereamigoingtoday(0)

Ooh ARCS specifiers, how quaint.
 
>  -Enda.

regards
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Paul Jakma	paul at clubi.ie	paul at jakma.org	Key ID: 64A2FF6A
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