rex@pangea.Stanford.EDU (Rex Sanders) (09/20/90)
Setup: Mac II with 80 Mb Rodime internal HD
new DPI 44R (Syquest) cartridge disk on external SCSI
internally terminated.
Problem: Turn OFF power to the DPI, but leave everything attached.
Power up Mac II.
BOOM - 80 Mb internal HD scrambled.
Spend 2-3 days recovering files using SUM II.
Could not recover from backups - that's what we attached the DPI for!
Repeated problem (accidentally) twice.
Called DPI - they were very apologetic, but said this was a "feature" of SCSI.
Said that some manufacturers had (expensively) engineered around this problem.
NO MENTION of this problem in (very slim) DPI manual.
I'm certain I've powered up a number of Mac IIs with non-DPI SCSI devices
turned off, including scanners, slide makers, CD-ROMs, and external hard disks.
I've never seen this problem before.
Is DPI, um, correct? How could BMUG recommend a drive with this "feature"?
-- Rex Sanders, USGS
rex@pmgvax.wr.usgs.govbmug@garnet.berkeley.edu (BMUG) (09/20/90)
In article <1990Sep19.175620.15824@morrow.stanford.edu> rex@pangea.Stanford.EDU (Rex Sanders) writes: > >(synopsis of problems with powered-down DPI drive on a powered-up Mac. > >How could BMUG recommend a drive with this "feature"? > Well, speaking on behalf of BMUG, we recommend the DPI because of all the Syquest drives we've seen, theirs has the most effective cooling. Most of the problems we've seen with Syquest media could be traced to overheating (sometimes the cartridges get almost too hot to touch with some other manufacturers' drives). We've also had the fewest reports of problems with DPI's drives. The problems that Rex noted are "features" of most SCSI drives, to the extent that the problem, in my opinion, is really Apple's (in the sense that it would be easiest for them to fix). I must say, though, that the most severe problem Rex related ("scrambling" the Mac's internal hard disk) is something I've never experienced after starting up my IIci with an internal Quantum 40 and a turned-off DPI drive. Rex, if you're a BMUG member -- I don't have our database handy just now :-) -- give Steve Costa a call on our help line and talk with him about it; you may have something else going on with your drive... John Heckendorn /\ BMUG ARPA: bmug@garnet.berkeley.EDU A__A 1442A Walnut St., #62 BITNET: bmug@ucbgarne |()| Berkeley, CA 94709 Phone: (415) 549-2684 | |
dplatt@coherent.com (Dave Platt) (09/22/90)
In article <1990Sep19.175620.15824@morrow.stanford.edu> rex@pangea.Stanford.EDU (Rex Sanders) writes: > Setup: Mac II with 80 Mb Rodime internal HD > new DPI 44R (Syquest) cartridge disk on external SCSI > internally terminated. > > Problem: Turn OFF power to the DPI, but leave everything attached. > Power up Mac II. > BOOM - 80 Mb internal HD scrambled. > Spend 2-3 days recovering files using SUM II. > Could not recover from backups - that's what we attached the DPI for! > Repeated problem (accidentally) twice. > > > Called DPI - they were very apologetic, but said this was a "feature" of > SCSI. Said that some manufacturers had (expensively) engineered around > this problem. NO MENTION of this problem in (very slim) DPI manual. > > I'm certain I've powered up a number of Mac IIs with non-DPI SCSI > devices turned off, including scanners, slide makers, CD-ROMs, and > external hard disks. I've never seen this problem before. > > Is DPI, um, correct? How could BMUG recommend a drive with this > "feature"? One of two things could be occurring here... one is easily correctable, the other isn't. [1] The DPI's SCSI interface (the actual bus-transceivers) may be "jamming the bus" when the drive's power is turned off. This is often due to the overvoltage/surge-protection circuit in the transceiver... it ties the bus-lines to the +5 power supply rail via a diode, in order to shunt off any spikes on the bus. When the drive is powered off, the +5 rail sinks down to ground, and the protective diode effectively short-circuits the bus. A design of this sort _is_ in compliance with the SCSI-1 standard, because the standard explicitly forbids having powered-off devices on the bus. It's generally acknowledged that this is an annoying design, however, and most manufacturers are switching to protective circuits which do allow the device to be powered down without shorting the bus. This problem is not easily correctable... it's inherent in the SCSI transeciver design. [2] The DPI's internal terminators are designed to accept power from the DPI's power supply. It's quite possible that these terminators _cannot_ also accept power from the SCSI bus if the DPI is turned off... that takes extra parts (one fuse, one diode, total parts cost less than half a buck). If this is the case, your SCSI bus will be misterminated if the DPI is off. This will seriously scramble data being sent over the bus; if your hard disk doesn't have parity-checking enabled, it could end up exhkuyrtinq gArvadge undt kerup!ingue@thu dusk. This problem is easily correctable. Remove the internal terminator resistors from the DPI (they'll be a set of two or three SIP or DIP resistor packs, plugged into sockets near the 50-pin ribbon cable header). Buy an external terminator, and plug it into the spare 50-pin CHAMP connector on the DPI case. External terminators will accept power from _any_ device on the bus... and the Mac II provides terminator power. If the DPI uses DB-25 connectors for its SCSI jacks (ugh!), then you may have grave difficulty finding an external terminator which will fit them. It's easier to buy a short DB25-to-CHAMP50 cable, plug it into the second DB-25 port, connect a CHAMP50 external terminator to the other end of the cable, and insulate the other side of the terminator with black electrical tape. I rather suspect that you've run into situation [2], and that switching to external termination will solve your problem.