Date: Sat, 2 Sep 1995 13:31:26 -0700 (PDT) From: "Rodney W. Grimes" <rgrimes@gndrsh.aac.dev.com> To: julian@ref.tfs.com (Julian Elischer) Cc: vernick@CS.SunySB.EDU, freebsd-hackers@FreeBSD.org Subject: Re: 4GB Drives Message-ID: <199509022031.NAA16013@gndrsh.aac.dev.com> In-Reply-To: <199509022024.NAA05005@ref.tfs.com> from "Julian Elischer" at Sep 2, 95 01:24:46 pm
next in thread | previous in thread | raw e-mail | index | archive | help
... > > Your thinking to simple, if the data was in the cache when the I/O > > hit the drive it would immediatly go to data phase preventing me from > > issuing another I/O to the next drive. I actually _dont_ want the > > drive to come on the bus yet. I need to be able to get all transfer > > operations to the drives before _any_ drive grabs the bus for a data > > transfer. This causes all drives to operate as a parallel unit. > > > > To simplify my problem with this I have gone to one drive per controller > > for developement purposes, but am still trying to work the issue of how > > do I make 4 drives on one bus all operate such that I can get the commands > > to all 4 drives before anyone of them grabs the bus for what is a rather > > long data transfer phase. > you can issue a SCSI seek command first to all the devices > then issue a read as a second round of commands > that way they will all give you instant response on the read > > seek1 > seek2 > seek3 > read1-data-phase > read2-data-phase > read3-data-phase. > > seek is command 2B, though it is an optional command.. Well, I could do that if I was at the drive level, but my code sits above the standard drivers, and actually just looks like another disk driver to the upper layers. I don't even know what scsi driver is doing the I/O as far as my code is concerned. The seek abstraction is missing from the layer between me and the driver :-(. ... -- Rod Grimes rgrimes@gndrsh.aac.dev.com Accurate Automation Company Reliable computers for FreeBSD
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?199509022031.NAA16013>