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From: =?utf-8?Q?Dag-Erling_Sm=C3=B8rgrav?= <des@des.no>
To: Alexander Motin <mav@FreeBSD.org>
References: <4BD06BD9.6030401@FreeBSD.org> <4BD099E6.6000402@FreeBSD.org>
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Date: Tue, 27 Apr 2010 16:16:29 +0200
In-Reply-To: <4BD6EDD6.8010403@FreeBSD.org> (Alexander Motin's message of
	"Tue, 27 Apr 2010 16:59:50 +0300")
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Cc: Maxim Sobolev <sobomax@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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Alexander Motin <mav@FreeBSD.org> writes:
> Dag-Erling Sm=C3=B8rgrav <des@des.no> writes:
> > 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.
> Have you ever seen them documented?

ISTR I got the info from sos@ at some point.  I have several Promise
cards lying around and was working onm RAID5 offloading, but I stopped
when ZFS became usable.

> Does the need to specifically handle dozens of incompatible
> implementations with limited resources worth those (probably not
> major) benefits?

The details probably vary from controller to controller, but the
capabilities are pretty much the same: perform the same write operation
to several disks at once, split a write operation across several disks,
compute and write parity.

IIRC, composite writes are already supported but not used.

DES
--=20
Dag-Erling Sm=C3=B8rgrav - des@des.no