Message-ID: <4548B13D.6070501@rtr.ca>
Date: Wed, 01 Nov 2006 09:37:49 -0500
From: Mark Lord <lkml@rtr.ca>
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To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Linus Torvalds <torvalds@osdl.org>, Jeff Garzik <jgarzik@pobox.com>,
       Conke Hu <conke.hu@amd.com>, linux-kernel@vger.kernel.org,
       linux-ide@vger.kernel.org, Andrew Morton <akpm@osdl.org>
Subject: Re: AHCI should try to claim all AHCI controllers
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Alan Cox wrote:
> Ar Maw, 2006-10-31 am 21:22 -0800, ysgrifennodd Linus Torvalds:
>> (We had the same issue with "PCI IDE controller". Some PCI IDE controllers 
>> are clearly exactly that from a programming interface standpoint, but 
>> because they support RAID in hardware, they claim to be RAID controllers, 
>> since that is more "glamorous". Gaah ;^).
> 
> Actually its far uglier than that. With one exception they don't support
> hardware raid mode, they use the RAID class tag to stop other OS drivers
> grabbing the interface or seeing it directly as un-raided software raid.

Note that a lot of the software raid controllers actually have full
hardware RAID acceleration in the chipset (single block command is automatically
remapped across several drives of a RAID 0/1/10 configuration, reducing bus
transactions and bandwidth requirements.

But they still require a driver do perform the RAID management,
and are thus not true "hardware" RAID.  But they are higher on the
food chain than total "pretend" RAID devices.

Cheers
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