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| Author | Multiple SCSI Hard Disks in a 7600 (Read 5263 times) | ||||||||||||||
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hellocharlie
2 MB  Posts: 2 
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on: November 07, 2007, 06:45
I've managed to set up a 7600 beautifully from all the info crammed on to these forums (thanks, all!). One big problem, though (aside from the dry-rotted plastic case parts snapping off)... I can't seem to get multiple HDs installed. When I connect two SCSI HDs the machine won't boot... it freezes up after the chime on a gray screen with the mouse cursor. I've managed to coerce one of my old 6100s to mount multiple drives by hotplugging one after the "Welcome to Mac OS" screen. Yeah, I know, bad idea... but I've initialized the (additional) disk in question with this method, so I know there's not a system folder or anything there to confuse the boot process. Any suggestions? My hardware configuration includes a CD-ROM, leaving one SCSI connection available. |
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wove
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1024 MB Posts: 1363
Reply #1 on: November 07, 2007, 15:23
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You are correct that hot plugging SCSI devices is a bad idea. Good to hear it worked this time around, but it is not a good habit. Problems with SCSI devices are most commonly related to two issues. The first is SCSI ids and the second termination. Every internal SCSI device must have a unique SCSI id. SCSI ids on hard drive are set with jumpers on the drive. SCSI itself have no rules for device numbering however by convention Macs typically use the following numbers. id 0 internal boot drive id 2 external scanner id 3 internal CD ROM id 5 internal ZIP drive id 7 SCSI controller on mother board On hard drives the SCSI id is set using jumpers. There are generally 3 jumpers that are set in a binary pattern to create the ids: ooo id 0 x00 id 1 oxo id 2 xxo id 3 oox id 4 xox id 5 oxx id 6 xxx id 7 Specifics for a drive can usually be found on the manufactures web site. Make sure each device has a unique id. Most likely the drive that came in the machine will be 0 and the CD will be 3. If the ribbon cable has more connections than there are devices it is best practice to have a device on the last connection leaving any unused connectors somewhere in the middle. The assigned id numbers have no impact on the devices placement on the cable. As long as the ids are unique it does not matter what order they are connected to the cable. The last device on a SCSI chain must be terminated. Termination is on or off and is set via another jumper. If this information is not on the drive itself it can again be found via searching on the web. The only area of confusion that exists regarding termination is that there is jumper refered to as "Enable termination power" and it is often confused with turning termination on or off. There is no reason for an internal device on a Mac to ever have the Enable Termination power jumper set. In sum. Insure that each device on the SCSI chain has a unique id number. Have the last (and only the last) device on the cable have termination turned on. bill
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performa_karma
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4 MB Posts: 6 
Reply #2 on: December 10, 2007, 13:08
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My internal ATA HD in my Performa 6300CD has apparently crashed as whenever I try to initialize is to put a fresh OS install on it it always says it failed (it doesn't even get past creating the root directory). I have an old internal Apple SCSI HD. Since it's an internal drive, it should already be set to SCSI ID 0, correct? Furthermore, if i attach it to the internal SCSI bus to which the CDROM drive is also attached will there be any SCSI termination issues? I assume the HD is self-terminating.
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wove
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1024 MB Posts: 1363
Reply #3 on: December 10, 2007, 14:11
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Quote from: "performa_karma" My internal ATA HD in my Performa 6300CD has apparently crashed as whenever I try to initialize is to put a fresh OS install on it it always says it failed (it doesn't even get past creating the root directory). I have an old internal Apple SCSI HD. Since it's an internal drive, it should already be set to SCSI ID 0, correct? Furthermore, if i attach it to the internal SCSI bus to which the CDROM drive is also attached will there be any SCSI termination issues? I assume the HD is self-terminating. Finding a used ATA hard drive is probably easier and cheaper than finding as SCSI drive. On machines with an ATA hard drive and a SCSI CD ROM, the internal SCSI is the older slower SCSI I and not the faster newer SCSI II. Without looking it is impossible to be sure what settings are on the CD or the hard drive. If it is still all factory settings on the CD then for that machine the CD would be SCSI id 3 and it will be terminated. For a stock hard drive it would probably be ID 0, however termination will vary depending on the machine it came from. Termination is not automatic on Macs and it will need to be set. Settings are often written on the label and if not the manufactures have data bases containing the settings for their drives. Termination is needed on the last device on the chain and only the last device on the chain. I think there are a number of posts in these forums that cover the topic in more detail. There are also many resources on the web that cover the details of the SCSI voodoo needed to keep Mac machines running swiftly. bill
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