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Re: [dm-devel] HPA unlock during partition scan of RAID components



Hello,

On Fri, Nov 04, 2011 at 11:42:20AM -0400, Phillip Susi wrote:
> On 11/4/2011 10:48 AM, Tejun Heo wrote:
> >I frankly don't care about BIOSen locking up afterwards and I don't
> >think they are more common than the issues from not unlocking (e.g.
> >moving harddrive to another machine, hot-plugging - partition -
> >reboot).  There will be a kernel param to disable unlocking behavior
> 
> Could you clarify what issues you refer to?  Moving a drive to
> another machine?

Yeah, that or hotplugging, or changing BIOS config, updating BIOS,
and, some (rare) BIOSen even fail to set up things consistently across
reboots.

> >and that would be it.  On top of that if bios is that screwed it's
> >probably a good idea to not use bios raid which is a silly thing to
> >begin with.  Currently the problem is that the kernel doesn't unlock
> >by default and the heuristics can't be turned off, so we have unhappy
> >customers on both sides.  Anyways, if md/dm people are on board, I'm
> >gonna push for that but otherwise there isn't much point.
> 
> It isn't only a problem for bios raid, it also affects mdadm raid.

Exposing alt size should be enough for md/dm no matter how hpa is
setup.

> Being able to defeat the heuristic would help, but I still don't see
> why the heuristic should be implemented in the kernel instead of
> user space?

Because sans raids, it was good enough and doesn't recent md's have
metadata at the beginning anyway?

The thing is that you have your problem, and other people have other
issues w/ HPA.  At this point, it's a misfeature abused by some silly
BIOSen mostly for silly BIOS raids.  I think we should expose the most
we can to our users and if some BIOSen are screwed on soft reboot,
well, just accept it or turn off HPA unlocking manually.

Thanks.

-- 
tejun


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