Re: disk geometry change

Doug Ledford (dledford@redhat.com)
Sat, 24 Apr 1999 12:36:17 -0400


Guest section DW wrote:
>
> The large disk howto says about aix7xxx:
>
> -----
> H=64, S=32 unless C < 1024, and moreover
> either the "extended" boot parameter was given,
> or the `extended' bit was set in the SEEPROM or BIOS,
> in which case H=255, S=63.
> -----
>
> This was true for 2.0.* and is still somewhat true for 2.2.6
> but the precise conditions have changed (and became messier).
> Two important changes are:
>
> For 2.0.36 giving boot parameters "aic7xxx=extended" would always
> give you an extended translation. For 2.2.6 this will only work
> if the driver finds no SEEPROM, but will be ignored otherwise.
>
> For 2.0.36, if the driver did not find a SEEPROM it would
> always give you an extended translation.
> For 2.2.6, if the driver did not find a SEEPROM it will
> only give you an extended translation if you asked for it.
>
> I do not know whether this change was intentional - it seems
> to me that a driver should do what the user asks in an explicit
> boot parameter. (Let me cc the maintainer.)
>
> Anyway, in your case the boot parameter "aic7xxx=extended"
> will probably work and give you an extended geometry again.
>
> Andries - aeb@cwi.nl
>
> P.S. Concerning LILO and unpleasant surprises:
> It is a good habit to always have several kernels in the LILO setup
> among which one known-to-be-good. That very much reduces the need
> for emergency boot floppies.

That latest driver allows the SEEPROM to override the user setting since
it makes no sense to not have them match. However, it *only* does this
when there are no partitions on the device, the latest code will always
take the geometry used in the partition table over its own geometry.
This makes things like swapping a disk between an NCR card and an
Adaptec card much easier. It also means that you should use the
"linear" option to lilo in cases where the partition geometry does not
match what the Adaptec BIOS wants to set for the disk or else you won't
be able to boot up properly.

-- 
  Doug Ledford   <dledford@redhat.com>
   Opinions expressed are my own, but
      they should be everybody's.

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