Date: Sun, 16 Jul 1995 16:25:38 -0500 (CDT) From: Karl Denninger <karl@Mcs.Net> To: terry@cs.weber.edu (Terry Lambert) Cc: karl@mcs.com, freebsd-hackers@freebsd.org Subject: Re: Twinchannel SCSI Adapter change Message-ID: <199507162125.QAA01860@Jupiter.mcs.net> In-Reply-To: <9507162104.AA15064@cs.weber.edu> from "Terry Lambert" at Jul 16, 95 03:04:30 pm
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> > I have changed the probe order on the twin channel SCSI 2742 adapter here to > > probe "b" first. > > [ ... ] > > > Anyone want these changes (move two lines) for the production code base, or > > does anyone else think this is a good (or bad) idea? > > A bad idea. > > EXAMPLE 1: > ------------------------------------------------------------------------- > I wish to reinstall a machine. > > I attach the CDROM drive I share between the machines in my lab > (maybe even a Sun CDROM drive?). > > I attempt to boot the CDROM (an external boot device). > > A bootable CDROM should be a possibility. Why do you believe that this is not possible? You ALREADY have to change the EISA configuration to do this. Therefore, you can certainly do this if you attach to the "A" channel, tell the system to boot from "A" in the EISA configuration, and that's that. Nothing prevents you from running the disk(s) on "A"; if there is nothing on "B" it does no damage. > ------------------------------------------------------------------------- > EXAMPLE 2: > ------------------------------------------------------------------------- > I want to be able to boot from an external disk if present, and if not, > boot from an internal disk instead. > > The purpose in doing this is OS cross developement for porting. > > It works like this: > > I detach a SCSI device from one machine and attach it to another. > > I write the boot and root file system information to the device. > > I detach the disk and return it to the first machine. > > I attempt to boot the first machine from the new image. > > If boot fails, I remove the disk from the first machine and boot the > installed OS on the internal drive and compare it with my code on the > second machine. > > I make corrections, and repeat the process. > ------------------------------------------------------------------------- > > The external device should be the first device checked, just as the > floppy should be the first checked. The second is a special case, and is easy to fix with an option for those who need it. 90% of the users aren't in this special case, and they are probably going to default to an internal drive. Since Adaptec has *known* problems with impedence matching when both the internal and external connectors are in use, its either/or on this one. -- -- Karl Denninger (karl@MCS.Net)| MCSNet - The Finest Internet Connectivity Modem: [+1 312 248-0900] | (shell, PPP, SLIP, leased) in Chicagoland Voice: [+1 312 248-8649] | 7 Chicagoland POPs, ISDN, 28.8, much more Fax: [+1 312 248-9865] | Email to "info@mcs.net" WWW: http://www.mcs.net ISDN - Get it here TODAY! | Home of Chicago's only FULL AP Clarinet feed!
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