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From: Scott Long <scottl@samsco.org>
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Date: Tue, 27 Apr 2010 08:49:26 -0600
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References: <4BD06BD9.6030401@FreeBSD.org> <4BD099E6.6000402@FreeBSD.org>
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	<4BD0ACD2.3040805@FreeBSD.org> <86och53tpl.fsf@ds4.des.no>
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Cc: Alexander Motin <mav@freebsd.org>,
	FreeBSD-Current <freebsd-current@freebsd.org>,
	Richard Tector <richardtector@thekeelecentre.com>, freebsd-geom@freebsd.org
Subject: Re: Switchover to CAM ATA?
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On Apr 27, 2010, at 7:34 AM, Dag-Erling Sm=F8rgrav wrote:
> Maxim Sobolev <sobomax@FreeBSD.org> writes:
>> Richard Tector <richardtector@thekeelecentre.com> writes:
>>> Could I also add that the removal of ataraid would affect those
>>> users who dual-boot with Windows and rely on the psuedo-raid
>>> provided by most Intel chipsets to be able to share the same pair of
>>> disks.
>> Well, this won't be a problem if we have GEOM classes that can
>> understand metadata created by the ATA RAID BIOS(es).
>=20
> Most pseudo-raid kit has nifty features like checksum offloading,
> composite writes etc. which can improve performance considerably.  You
> can't access those from GEOM.

If my "most" you mean "a small subset of vendors and products", then =
yes, you're correct.  For the vast remaining majority, all you get is a =
special BIOS that can do striping and mirroring at boot.  Sometimes that =
special BIOS requires a special hook in the controller chip, which is =
why you have ICHxxR vs ICHxx chips, for example.  All the 'R' means is =
that the silicon supports an external ROM.

Scott