[dm-devel] Re: [PATCHSET] block,scsi,libata: implement alt_size

[Dan Williams]

On Mon, May 4, 2009 at 1:02 AM, Tejun Heo <tj at kernel.org> wrote:
>> Couldn't the "fix" also just be a note to users to disable ignore_hpa
>> if they notice that there raid arrays are not assembling correctly?
>
> I don't know.  If it doesn't work automatically, the solution really
> isn't worth much.  People generally don't (shouldn't need to) have any
> idea what HPA is.  It basically boils down to "Linux doesn't support
> RAID".  :-)
>
> Maybe we should just put this issue to the rest and strongly advise
> people against BIOS raids.

That's a bit too far :-).  The real issue is that Linux is ignoring a
property of the platform.  To me ignoring HPA is like ignoring an e820
reserved memory region.  You might be able to get away with it
sometimes, but other times it breaks.

However, in the end I think having 'alt_size' available is a useful
mechanism for discovering and handling the ignore_hpa=1 case.   The
policy about when to trust it can be left to userspace.

Thanks,
Dan