Re: installation problem

[David Laight <david%l8s.co.uk@localhost>]

On Fri, Jul 03, 2015 at 06:26:09PM -0400, Greg Troxel wrote:
> 
> Robert Elz <kre%munnari.OZ.AU@localhost> writes:
> 
> >     Date:        Fri, 3 Jul 2015 17:09:15 +0100 (BST)
> >     From:        steve%prd.co.uk@localhost (Steve Blinkhorn)
> >     Message-ID:  <20150703160916.5D2031E488%body.prd.co.uk@localhost>
> >
> > What's this supposed to be?
> >
> >   | 16 partitions:
> >   | #        size    offset     fstype [fsize bsize cpg/sgs]
> >   |  a: 976773167         1     4.2BSD   4096 32768     0  # (Cyl.      0*- 1033622*)
> >   |  c: 976773167         1     unused      0     0        # (Cyl.      0*- 1033622*)
> >   |  d: 976773168         0     unused      0     0        # (Cyl.      0 - 1033622*)
> >
> > I am fairly sure that you need to allow more than 1 block for the 2nd stage
> > boot loader to fit.   Your other disc used the common, but meaningless, 63
> > as the start offset for a & c partitions.   Better (though it might not matter
> > on those drives) would be a power of 2 (or at least, a multiple of 8).  32
> > should work fine.   
> 
> You do need more, nominally 14, but the 2nd stage loader goes in blocks
> 2-15 of the root filesystem partition.  Still, the use of offset 1 is
> irregular and risks testing unused code paths, which is recommended only
> if you want to encounter and fix new obscure bugs for the greater good.

Some 1st stage bootloaders assume they can use more than 1 sector,
and I think some boot sector virus protection 'stuff' can use other
sectors in the first track.

> In all seriousness, on x86, use 64 for a filesystem or raid at a these
> days, in order to avoid misalignment of 4K native sectors.

Some modern partitioning tools reserve 1MB.
I've used that space to add a boot partition to a USB stick.
Finding an mbr editor that would let me do that wasn't trivial.
I think I was the one that stopped the netbsd one letting me do it!

	David

-- 
David Laight: david%l8s.co.uk@localhost