harrison@csl.dl.nec.com (Mark Harrison) (05/24/91)
We have a portable scsi qic-150 tape drive that we share among
several users. We basically use it when we have some installs
or private backups and want to do the work at our desks instead
of standing in the machine room.
Most of this is done on diskless workstations (Sun SLC's), and we
freely plug and unplug the tape drive.
There has been some concern over a regular workstation (Sparc 1+)
that has an additional external scsi hard disk. For some reason,
we are under the impression that to hook the tape drive to that
machine, we have to bring the machine down, unhook the disk drive,
plug the tape drive to the machine, and then daisy-chain the disk
drive to the tape drive. I think whoever came out and installed
the thing had it set up that way, and nobody (including me :-)
wants to take the blame for screwing things by trying it differently.
My questions:
1. Is there *any* significance to the order of daisy chaining?
2. Is it safe to plug and unplug the tape drive while the system
is up?
3. (this is the point of the whole posting) Will I screw things
up if I simply plug and unplug the tape drive into the disk
drive while the system is running?
4. What FM should I be reading to know about this stuff?
Thanks in advance,
Mark.
--
Mark Harrison | Note: harrison@ssd.dl.nec.com and
harrison@csl.dl.nec.com | necssd!harrison are not operating at
(214)518-5050 | present. Please forward mail through the
| above address. Sorry for the inconvenience.scs@iti.org (Steve Simmons) (05/24/91)
harrison@csl.dl.nec.com (Mark Harrison) writes: >There has been some concern over a regular workstation (Sparc 1+) >that has an additional external scsi hard disk. For some reason, >we are under the impression that to hook the tape drive to that >machine, we have to bring the machine down, unhook the disk drive, >plug the tape drive to the machine, and then daisy-chain the disk >drive to the tape drive. I think whoever came out and installed >the thing had it set up that way, and nobody (including me :-) >wants to take the blame for screwing things by trying it differently. >My questions: >1. Is there *any* significance to the order of daisy chaining? Yes. A SCSI bus requires that the *end* of the chain be terminated, ie, have some special resistors on it. If those resistors are missing, you may get bus errors. There are two ways to terminate. Most scsi devices have a plug that a resistor pack can be placed into. This terminates the SCSI bus in the device. It's usually referred to as an internal terminator. More and more you'll see external SCSI terminators -- a device that plugs into one of the SCSI sockets outside the device. These cost more ($40?) but are much more flexible. Note that if you have an internal terminator, that's the end of the bus. If you add devices further down the chain, they won't be seen. >2. Is it safe to plug and unplug the tape drive while the system > is up? Suns seem to be fairly insensitive to removing the terminator for short periods. We regularly remove/add tape drives on 3/50s, 3/60s, and IPCs *if* they are the last thing on the bus. Disconnect a disk and your system will crash almost immediately. We've also moved DEC SCSI TK-50s from system to system without problem. >3. (this is the point of the whole posting) Will I screw things > up if I simply plug and unplug the tape drive into the disk > drive while the system is running? It depends. As mentioned above, I've had good luck on specific systems. But it has been claimed on some systems if a device is not on the bus at boot time, it cannot be added later. Sorry, can't confirm or deny. >4. What FM should I be reading to know about this stuff? If you find one, let us *all* know. -- "If we don't provide support to our users someone is bound to confuse us with Microsoft." -- Charles "Chip" Yamasaki
de5@ornl.gov (Dave Sill) (05/24/91)
In article <1991May24.143831.10687@csl.dl.nec.com>, harrison@csl.dl.nec.com (Mark Harrison) writes: > >1. Is there *any* significance to the order of daisy chaining? No. >2. Is it safe to plug and unplug the tape drive while the system > is up? No. >3. (this is the point of the whole posting) Will I screw things > up if I simply plug and unplug the tape drive into the disk > drive while the system is running? Maybe, maybe not. You certainly *could* mess things up. >4. What FM should I be reading to know about this stuff? I don't know, but I wish I'd read a copy of it before I took the course on SCSI fiddling from the School of Hard Knocks. In my experience, the only safe way to reconfigure SCSI devices is with the power off on *all* devices, including the system. -- Dave Sill (de5@ornl.gov) It will be a great day when our schools have Martin Marietta Energy Systems all the money they need and the Air Force Workstation Support has to hold a bake sale to buy a new bomber.
david@talgras.UUCP (David Hoopes) (05/27/91)
In article <1991May24.143831.10687@csl.dl.nec.com> harrison@csl.dl.nec.com (Mark Harrison) writes: >We have a portable scsi qic-150 tape drive that we share among > [stuff deleted] >My questions: > >1. Is there *any* significance to the order of daisy chaining? > yes and no. No, the order of devices dosn't matter. Yes, the terminator must be at the end of the chain. Some devices have internal terminators. If one of the devices you have has an internal terminator then it must be the last device in the chain. >2. Is it safe to plug and unplug the tape drive while the system > is up? We do this all the time around here (we develope for scsi products). We manage to blow up host adapters on a fairly regular basis. All we have to do is walk to the other end of the building and have them repaired so we don't worry about it to much. > >3. (this is the point of the whole posting) Will I screw things > up if I simply plug and unplug the tape drive into the disk > drive while the system is running? Yes! You would probably get away with it for awhile but sooner or later something would die. -- --------------------------------------------------------------------- David Hoopes Tallgrass Technologies Inc. uunet!talgras!david 11100 W 82nd St. Voice: (913) 492-6002 x323 Lenexa, Ks 66214