Date: Fri, 3 May 1996 21:27:35 -0700 (PDT) From: "Rodney W. Grimes" <rgrimes@GndRsh.aac.dev.com> To: vernick@CS.SunySB.EDU (Michael Vernick) Cc: scsi@freebsd.org Subject: Re: Adaptec 3940 and Scatter/Gather Message-ID: <199605040427.VAA00731@GndRsh.aac.dev.com> In-Reply-To: <199605032215.SAA18813@cs.sunysb.edu> from Michael Vernick at "May 3, 96 06:15:45 pm"
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> The documentation specifies that the 3940 can perform scatter/gather. As can the aha(1542, 1742, 2742, 2940, 2842), bt(542, 742, 747, 757, 946), etc etc... > Does anyone know how to use this feature? FreeBSD uses it on all the above cards, read the source code to understand how it is used. > Is it Adaptec specific? No, almost all bus master scsi controllers support scatter/gather. > I didn't see anything about scatter/gather in the Scsi spec. It has nothing to do with the scsi bus, it has to do with the fact that you can gather arbitrary blocks of host memory into one write command, or scatter one scsi read command to many memory blocks. This is very advantages when your I/O subsystem runs using physical addresses and the host OS is a virtual memory system. -- Rod Grimes rgrimes@gndrsh.aac.dev.com Accurate Automation Company Reliable computers for FreeBSD
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