Date: Sun, 16 Jul 95 15:04:30 MDT From: terry@cs.weber.edu (Terry Lambert) To: karl@mcs.com (Karl Denninger, MCSNet) Cc: freebsd-hackers@freebsd.org Subject: Re: Twinchannel SCSI Adapter change Message-ID: <9507162104.AA15064@cs.weber.edu> In-Reply-To: <m0sXXIY-0003kwC@mercury.mcs.com> from "Karl Denninger, MCSNet" at Jul 16, 95 12:16:10 pm
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> Good afternoon, > > I have changed the probe order on the twin channel SCSI 2742 adapter here to > probe "b" first. > > The reason is this: > > 1) "A" has both internal and external connectors. > 2) "B" has only an internal connector. > > You probably will want to boot from an internal disk drive, or if you do > not, you probably want to have ALL disks external. > > If you boot from an internal disk, there is no reason not to use it on > channel "B". > > If you have an internal and external disk setup, why not boot from "B" and > have your externals on the only available connector -- "A"? This reduces > adapter contention and improves performance. [ ... ] > 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. ------------------------------------------------------------------------- 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. Terry Lambert terry@cs.weber.edu --- Any opinions in this posting are my own and not those of my present or previous employers.
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