tonyrich@titanic.cs.wisc.edu (Anthony Rich) (06/08/90)
I recently put together a Teac 150MB SCSI tape backup unit by mounting a raw Teac N50 drive in a 5.25" enclosure/power supply. I've connected it directly to my Mac II and I use Retrospect to back up my internal CDC/Imprimis 300MB hard drive onto tape. The tape drive works properly. But after doing a backup, if I turn the Teac off while the Mac is still on, the Mac crashes on the first mouse double-click and won't reboot from the hard drive; the floppy with the flashing question mark comes up. Then if I boot from a floppy, either the hard drive isn't mounted at all or a dialog comes up with a picture of the hard disk that says "This disk is damaged; do you want to erase it?" But if I turn the Teac tape unit back back on and reboot, the hard disk WILL then be recognized (even if I haven't repaired it with SUM II yet) and the Mac will reboot from it, although it takes a while because apparently some built-in filesystem check-and-repair is done to correct the hard disk's "damage" before the "Welcome to Macintosh" message comes up. 1. Is this normal behavior for a Teac 150MB tape backup unit connected to a Mac II? Shouldn't I be able to turn the tape drive off while the Mac is on without crashing the Mac? 2. Since I only do a tape backup occasionally, I don't want to leave the tape drive on forever, although I normally leave the Mac running all the time. Is there some way I can tell the Mac that I'm done with the Teac so that I can safely shut the tape drive off without turning off the Mac? 3. Is there a switch or some other hardware on the tape drive that I can or should have modified that will fix the problem? I don't think it's a SCSI termination problem, but correct me if I'm wrong. It's my understanding that the Teac N50 has its own internal termination, and presumably so does the (internal) Wren IV hard drive, so I haven't added any SCSI terminators, and the tape drive itself functions perfectly. When I put a Microtek 300Z scanner in the SCSI chain between the tape drive and the Mac, again with no extra termination, there is no change in behavior; turning off the tape drive crashes the Mac. However, I can turn the scanner (and its special SCSI adapter box) on and off while the Mac is on with no problems whatsoever. Why can't I do that with the tape drive? Thanks in advance for any suggestions. -- ----------------------------------------- | EMAIL: tonyrich@titanic.cs.wisc.edu | | Disclaimer: I speak only for myself. | -----------------------------------------
kaufman@Neon.Stanford.EDU (Marc T. Kaufman) (06/08/90)
In article <10567@spool.cs.wisc.edu> tonyrich@titanic.cs.wisc.edu (Anthony Rich) writes: >1. Is this normal behavior for a Teac 150MB tape backup unit connected to > a Mac II? Shouldn't I be able to turn the tape drive off while the > Mac is on without crashing the Mac? >I don't think it's a SCSI termination problem, but correct me if I'm wrong. >It's my understanding that the Teac N50 has its own internal termination, >and presumably so does the (internal) Wren IV hard drive, so I haven't added >any SCSI terminators, and the tape drive itself functions perfectly. Au contraire. It is definitely a SCSI termination problem. SCSI terminators require power. Generally, with internal termination, that power is provided by the device (and only a very few devices will also allow the ternimators to be powered from the bus). When you turn off the device, you turn off the terminator power, and effectively short all of your SCSI bus lines to ground (through 135 ohms). The answer is to remove the internal termination from the Teac, and add an external terminator (which will take power from the Mac II). Marc Kaufman (kaufman@Neon.stanford.edu)
dplatt@coherent.com (Dave Platt) (06/09/90)
In article <10567@spool.cs.wisc.edu> tonyrich@titanic.cs.wisc.edu (Anthony Rich) writes: > I recently put together a Teac 150MB SCSI tape backup unit by mounting a > raw Teac N50 drive in a 5.25" enclosure/power supply... > > But after doing a backup, if I turn the Teac off while the Mac is still on, > the Mac crashes on the first mouse double-click and won't reboot from the > hard drive; the floppy with the flashing question mark comes up. Then if > I boot from a floppy, either the hard drive isn't mounted at all or a > dialog comes up with a picture of the hard disk that says "This disk is > damaged; do you want to erase it?" I'd be interested to see if the disk would be recognized properly if you were to power down the Mac II (with the pushbutton switch in back), wait a minute or so, and then power it back up. Cycling the power will reset the SCSI-bus hardware in a way which a crash-and-reboot will not; it'll also reset the internal hard disk. > But if I turn the Teac tape unit back back on and reboot, the hard disk > WILL then be recognized (even if I haven't repaired it with SUM II yet) and > the Mac will reboot from it, although it takes a while because apparently > some built-in filesystem check-and-repair is done to correct the hard disk's > "damage" before the "Welcome to Macintosh" message comes up. This checkout process is performed if the Mac "mounts" a volume, and sees that the "I'm in use and have not been dismounted cleanly" flag is set. HFS checks the directory structures, and makes certain that all extents mentioned by any accessible file are marked "in use" in the extent allocation bitmap. This checking process won't perform any extensive repairs, but it does ensure that you won't end up allocating the same disk block to two different files. > 1. Is this normal behavior for a Teac 150MB tape backup unit connected to > a Mac II? Shouldn't I be able to turn the tape drive off while the > Mac is on without crashing the Mac? This is not normal behavior. I'm using a very similar setup... Mac II, with a Teac N50 in an external drive case (there's also a Toshiba CD-ROM mechanism in the same box); internal termination packs on the Teac controller board. I can run a backup or restoration using ExpressTape (nee Nuvo Labs FastTape), and then turn off the power to the external box; the Mac does not crash. The Mac _will_ hang if I've used the CD-ROM drive during the current session... the Toshiba/OMI CD-ROM driver periodically polls the drive to see if a new disc has been inserted, and these SCSI polls will hang up and time out if the drive is turned off. This is not a problem with the tape drive, however, since it isn't polled unless ExpressTape is running. > 3. Is there a switch or some other hardware on the tape drive that I can > or should have modified that will fix the problem? I don't believe it's a hardware-configuration problem. Certainly, I've never seen such problems in my setup, and I haven't done any reconfiguration on my drive. Here's my guess: I seem to remember hearing that the new version of Retrospect comes with an INIT that patches the SCSI Manager, and gives Retrospect the ability to use the disconnect/reconnect capability of the tape drive (that is, send a block of data to the drive controller, instruct the drive to disconnect from the SCSI bus, and then reconnect when the controller buffers begin to get empty). This allows Retrospect to overlap disk accesses with tape motion, and speeds up the backup process. I have a hunch that Retrospect's use of this facility is somehow leaving the SCSI bus in a strange state. Perhaps the modified SCSI Manager is occasionally polling the tape drive, and is becoming sadly confused if the drive vanishes from the bus. Perhaps the Mac's SCSI controller chip is being left in an unstable condition. Perhaps it's the phase of the moon ;-}. If Retrospect does come with an overlapped-I/O INIT or Control Panel device, I suggest that you remove it; if the use of overlapped I/O is a Retrospect configuration option, try turning it off. Then reboot (even better, shut down and then power-up again), do a backup, eject the tape, turn the drive off, and see if the problem still remains. I think there's a fair chance it will have gone away. If this fails, try using a different backup utility... ExpressTape or FastTape, rather than Retrospect. > I don't think it's a SCSI termination problem, but correct me if I'm wrong. > It's my understanding that the Teac N50 has its own internal termination, > and presumably so does the (internal) Wren IV hard drive, so I haven't added > any SCSI terminators, and the tape drive itself functions perfectly. You are correct... the N50 has internal terminators. The Teac is fairly sensitive to proper termination. I tried using an external terminator with my external drive box (for flexibility, so that I could remove termination if I wanted to), and the terminator or cable wasn't making good electrical contact... the Toshiba CD-ROM drive would show up in a SCSIProbe inquiry, but the Teac wouldn't respond properly... SCSIProbe could tell that there was something at that address, but said "No data available" or "Device busy". > When I put a Microtek 300Z scanner in the SCSI chain between the tape drive > and the Mac, again with no extra termination, there is no change in behavior; > turning off the tape drive crashes the Mac. However, I can turn the scanner > (and its special SCSI adapter box) on and off while the Mac is on with no > problems whatsoever. Why can't I do that with the tape drive? You should be able to. I suppose it's possible that turning off the external drive is somehow putting a power-surge on the SCSI bus and is scrambling the bus... but I haven't seen that sort of problem with my Teac. -- Dave Platt VOICE: (415) 493-8805 UUCP: ...!{ames,apple,uunet}!coherent!dplatt DOMAIN: dplatt@coherent.com INTERNET: coherent!dplatt@ames.arpa, ...@uunet.uu.net USNAIL: Coherent Thought Inc. 3350 West Bayshore #205 Palo Alto CA 94303
dplatt@coherent.com (Dave Platt) (06/09/90)
In article <1990Jun8.150226.22946@Neon.Stanford.EDU> kaufman@Neon.Stanford.EDU (Marc T. Kaufman) writes: > Au contraire. It is definitely a SCSI termination problem. SCSI terminators > require power. Generally, with internal termination, that power is provided > by the device (and only a very few devices will also allow the ternimators > to be powered from the bus). The Teac is one of these devices... its internal terminators will accept power from the bus if the Teac is powered off. It's a good design (diode and fuse to +5, provides power to the bus, will accept power from the bus, and if you manage to short pin 25 to ground you'll blow the fuse but won't lose power to the internal terminators as long as the device is powered up). I wish all SCSI implementors used circuitry of this sort. It's entirely possible to boot a Mac and use the SCSI bus if you have a powered-down Teac N50 attached to the bus, as long as you're using the Teac's internal terminators and have some other device (such as the Mac) providing power to the bus. Trust me... I do it all the time. > The answer is to remove the internal termination from the Teac, and add an > external terminator (which will take power from the Mac II). I really doubt that this will make a difference. I'm using a hardware setup almost identical to Tony's, and its terminators are perfectly happy. -- Dave Platt VOICE: (415) 493-8805 UUCP: ...!{ames,apple,uunet}!coherent!dplatt DOMAIN: dplatt@coherent.com INTERNET: coherent!dplatt@ames.arpa, ...@uunet.uu.net USNAIL: Coherent Thought Inc. 3350 West Bayshore #205 Palo Alto CA 94303