linux-kernel - Re: [PATCHSET] block,scsi,libata: implement alt

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Date:	Tue, 05 May 2009 12:28:53 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Dan Williams <dan.j.williams@...il.com>
CC:	Jeff Garzik <jeff@...zik.org>, linux-ide@...r.kernel.org,
	jens.axboe@...cle.com, linux-kernel@...r.kernel.org,
	linux-scsi@...r.kernel.org, James.Bottomley@...senpartnership.com,
	Mauelshagen@...hat.com, dm-devel@...hat.com
Subject: Re: [PATCHSET] block,scsi,libata: implement alt_size

Hello,

Dan Williams wrote:
> On Mon, May 4, 2009 at 1:02 AM, Tejun Heo <tj@...nel.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.

Well, somewhat but not quite.  The difference is with backward
compatibility and the fact that HPA has been used for many different
creative ;-) purposes including working around BIOS limitations.

> 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.

Pushing this in the kernel without updating dm-raid is kind of
pointless.  Who should I be poking to get the userland part moving?

Thanks.

-- 
tejun
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