Date: Fri, 21 Apr 1995 09:56:52 -0400 (EDT) From: Peter Dufault <dufault@hda.com> To: wilko@yedi.iaf.nl (Wilko Bulte) Cc: terry@cs.weber.edu, pritc003@maroon.tc.umn.edu, rgrimes@gndrsh.aac.dev.com, hackers@freefall.cdrom.com Subject: Re: [DEVFS] your opinions sought! Message-ID: <199504211356.JAA16639@hda.com> In-Reply-To: <199504201827.UAA01354@yedi.iaf.nl> from "Wilko Bulte" at Apr 20, 95 08:27:20 pm
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Wilko Bulte writes: > > > 2) Automatic generation/removal of devices on bus reset. For > > instance, attach a device to the SCSI device chain, or > > power on a tape on the chain that was not powered on at > > boot time, and it can be made available. The existance > > of a device file is no longer an ambiguous marker. > > Yuck! Powering up/down for SCSI devices on the fly is generally a > sure way to hang the buses, screw the disks etc. It *should* work, > but my experience shows that it has something like a 20% chance to > bomb. > This is true, though with practice you only have to restore your disks once a year. We still have a nasty bug someplace that results in unending disk timeouts and eventual system death. Usually, though our disk drivers will redo a transfer that was in progress when a device powered up on the bus, assuming the disk drive properly detects the power up. A utility that suspends all activity on the SCSI bus will make powering up a device safe, though, and I've been thinking of doing it (suspend activity, beep when all activity is suspended, delay for 10 seconds, and permit activity to resume). To be honest I power things up on the bus all the time. I also do backups at night. -- Peter Dufault Real Time Machine Control and Simulation HD Associates, Inc. Voice: 508 433 6936 dufault@hda.com Fax: 508 433 5267
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