Re: current best practice for booting >2TiB volumes?

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

On Sun, Feb 20, 2011 at 10:57:27PM -0600, Eric Schnoebelen wrote:
> 
> David Laight writes:
> - On Fri, Feb 18, 2011 at 06:28:34PM -0500, Matthew Mondor wrote:
> - > On Fri, 18 Feb 2011 12:09:39 -0600
> - > eric%cirr.com@localhost (Eric Schnoebelen) wrote:
> - > 
> - > > When I attempt to boot (after relocating wd2/3 to wd0/1), the gpt
> - > > mbr loads bootxx_ffsv1, but bootxx_ffsv1 complains it can't find
> - > > /boot in the root filesystem.
> - 
> - The bootxx code probably requires that to root fs be at the start of
> - the raid volume.
> 
> Hmm, that might be the problem.  I was treating it like a wdXa,
> where the NetBSD partion starts at 64 (offset 63).  I'll try
> recreating the FS with root starting at offset 0.

The RF 'disk' is usually formatted like a bios partition.
So sector 1 is a disklabel (etc).
(but the boot code won't look at it).

> - It might also get confused by any disklabel in the pbr (presumably
> - you don't have one).
> 
> installboot(8) does complain about there being no pbr..

Installboot adds the code to the pbr! It avoids writing to the sector
that might contain a label.

> - Certainly 'boot from RF' relied on the bootxx code adding in 64 sectors
> - and trying again after an initial file open failed.
> -
> - But I can't remember if this was in any way related to detecting
> - an RF entry in the pbr's disklabel.
> - 
> - Your disks may have larger physical sectors. So you really want
> - to align the fs fragments/blocks onto physical sectors. The offset
> - 63 sector offset (one nominal track) isn't a good value!
> 
> I was reading that as offset of 63, with sectors 0-63 (aka 64)
> being unused, and sector 64 being the first sector of my
> partion.
> 
> Am I mis-interpreting?

Yes - the offset of 63 means that that sectore 0-62 are unused.
I (think it was me) changed the default offsets for large volumes
to be 1M (and 1M alignments) instead of track/cylinder alignment.


        David

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