ireland@ac.dal.ca (05/26/90)
I posted a message a few days ago explaining a problem I was having daisy- chaining two external SCSI drives to my MacPlus. One of the drives is a Jasmine 70 (Rodime mechanism), the other is a LaCie Cirrus 45 (Seagate mechanism). Both drives work fine individually, but I couldn't boot the Mac when they were both connected at the same time. I kept getting a SadMac icon. Changing the SCSI number assignments had no effect. I want to thank all the people that responded to my question and offered suggestions, but I'm confused by some of these suggestions and would like more information. One person said that Rodime's are non-standard SCSI devices and have problems working with other drives sometimes. Another person said I might have to use the startup cdev to set the drive that I wanted to be the startup drive. I have daisy chained drives before without using the startup cdev and am not sure what is for. A third person said there could be a problem if both drives had system/finders installed. I don't believe this is a problem. All the rest (six) said I had a termination problem, and that only the last drive in the daisy chain was supposed to be terminated. Is this right? In my Jasmine Owner's Guide, it says that both ends of the chain are to be terminated, so one doesn't start removing terminators until the third SCSI device is added. What's the scoop on terminators? One at the end or one at each end? Thanks, Keith Conover Keith@ac.dal.ca
robbins@rice.edu (Thomas Robbins) (05/30/90)
In article <1654@ac.dal.ca> ireland@ac.dal.ca writes: \I posted a message a few days ago explaining a problem I was having daisy- |chaining two external SCSI drives to my MacPlus. One of the drives is a /Jasmine 70 (Rodime mechanism), the other is a LaCie Cirrus 45 (Seagate -mechanism). Both drives work fine individually, but I couldn't boot the \Mac when they were both connected at the same time. I kept getting a |SadMac icon. Changing the SCSI number assignments had no effect. [deleted] /All the rest (six) said I had a termination problem, and that only the last -drive in the daisy chain was supposed to be terminated. Is this right? \In my Jasmine Owner's Guide, it says that both ends of the chain are to be |terminated, so one doesn't start removing terminators until the third SCSI /device is added. What's the scoop on terminators? One at the end or one at -each end? \ |Thanks, Keith Conover /Keith@ac.dal.ca Your confusion here is caused by the fact that the Macintosh itself is one "end" of the daisy chain, with its own internal termination. You therefore start removing terminators once the **second** SCSI device is added. Your first SCSI device is actually the middle of the daisy chain, and having an external terminator attached to that device will do many interesting things to your Mac, none of them good. -- Tom Robbins | Youth is wasted on the young. robbins@owlnet.rice.edu | - George Bernard Shaw Senior, Chemical Engineering | Life is wasted on the living. Rice University | - Zaphod Beeblebrox IV
arends@metaphor.metaphor.com (Dale M Arends) (05/30/90)
In article <1654@ac.dal.ca> ireland@ac.dal.ca writes: [ stuff deleted ] >All the rest (six) said I had a termination problem, and that only the last >drive in the daisy chain was supposed to be terminated. Is this right? >In my Jasmine Owner's Guide, it says that both ends of the chain are to be >terminated, so one doesn't start removing terminators until the third SCSI >device is added. What's the scoop on terminators? One at the end or one at >each end? > >Thanks, Keith Conover >Keith@ac.dal.ca It is really confusing the way documentation reads concerning terminators. Simply put, only the first and last devices on the bus should have terminators. The thing to remember is that the SCSI ID numbers are irrelevant in this. It is the first and last PHYSICAL CONNECTIONS that require terminators and NO INTERMEDIATE DEVICES GET TERMINATORS. So we have the following: 1 internal drive or 1 external drive Terminate it! 1 internal drive and 1 external drive Terminate both! no internal drive and 1 external drive Terminate it! no internal drive and n external drives Terminate FIRST and LAST external 1 internal drive and n external drives Terminate internal and LAST external That's all there is to it (except finding out how to remove terminators if necessary.) The SCSI ID numbers are useful (from a user standpoint) to determine the startup device. The internal drive should always be ID 0, the Mac is ID 7 and the IDs 1-6 are available to use for devices. Oh yeah, the chain is scanned in reverse order so if the selected startup device has number 6, the system may startup a little quicker. Hope this clears things up. Dale ------------------------------------------------------------------------------- Dale M. Arends Metaphor Computer Systems, Inc. arends@metaphor.com Any opinions expressed herein are my own and not those of my employer. They probably aren't interested and maybe don't agree and therefore ...
etxtorn@juno11.ericsson.se (Thomas Tornblom Konsult TM/JU 99367) (05/31/90)
In article <8257@brazos.Rice.edu> robbins@owlnet.rice.edu (Thomas Robbins) writes: >In article <1654@ac.dal.ca> ireland@ac.dal.ca writes: > [deleted] >/All the rest (six) said I had a termination problem, and that only the last >-drive in the daisy chain was supposed to be terminated. Is this right? >\In my Jasmine Owner's Guide, it says that both ends of the chain are to be >|terminated, so one doesn't start removing terminators until the third SCSI >/device is added. What's the scoop on terminators? One at the end or one at >-each end? >\ >|Thanks, Keith Conover >/Keith@ac.dal.ca > >Your confusion here is caused by the fact that the Macintosh itself is one >"end" of the daisy chain, with its own internal termination. You therefore >start removing terminators once the **second** SCSI device is added. Your >first SCSI device is actually the middle of the daisy chain, and having >an external terminator attached to that device will do many interesting >things to your Mac, none of them good. Well, the mac+ is kind of an exception in the sense that it lacks internal SCSI termination. Therefore the first AND the last SCSI unit should be terminated and no other unit. All macs with built-in HD have the drive terminated and needs termination only in the last unit in the external chain.