Ultra SCSI drives and old Macs

[haemogoblin]

Hi everyone

I bumbled my first post by putting it in the Nubus section by accident, instead of PCI mac. That will teach me for using my phone! lol

I have 7x Hitachi Ultrastar Ultra320 73GB SCSI drives, which a friend gave me recently. I tried getting one to work on my Powermac 8500, using a 80pin to 50pin adapter. The only problem is, the computer doesn't see the drive at all. I tried all sorts of configurations, but nothing seemed to work

CelGen reply to my initial thread, saying the following; "Most of the high capacity SCSI drives dropped support for the older SCSI-1/SCSI-2/FastSCSI buses"

I'm using an ultra SCSI drive atm, but it is only an 9GB IBM drive and no where near as big as the Hitachi's. Going on what CelGen said, does this mean the only way to get a large capacity drive working on the PM is via a SCSI controller card?

I would really appreciate advice on this as having a little more storage space would be very handy. A single 73gb drive would solve all my storage problems period.

Cheers

 

[CelGen]

I stand by what I say. It varied from manufacturer to manufacturer but eventually it came down to the vendor simply dropping support for the older SCSI chains. the SCA adapters were fine when we were still attaching them to 9 and 18gb drives but compatibility seemingly fell off a cliff a few years ago. Something like the mac 2940WU will support these newer drives because they have a native UltraSCSI bus on them. My WGS95 has five HD68 pinned UltraSCSI disks in it running off an Atto SE IV and you can clearly tell that the performance is better than when I used the internal SCSI bus.

 

[Compgeke]

Check the termination. You *need* a terminator when using SCA drives otherwise they won't show up, or if they do they freeze a lot. Other than that and making sure the ID is set (on adapter board or drive, not both), the drives are probably just incompatible. 

It's all just a crapshoot, I've had 146 gig Seagate drives work but some 4.6 gig Western Digitals won't. 

 

[Bunsen]

It really comes down to finding the manufacturer's specs for each specific drive model, and seeing if they support SCSI-1.  In general, people seem to report more success with Ultra-160 drives than Ultra-320.  Then and only then is it worth worrying about adapters and termination.

/moved to Peripherals/

 

[haemogoblin]

Thanks guys, really appreciate the input.

 

[max1zzz]

Some SCA drives need the upper 8 bits of the data bus terminated before they will work (and as others have said, some just won't work at all)

I used to make adapters that did this, but don't have the time to anymore. If you're handy with a soldering iron you could just solder the required resistors to the 50 - > 80 pin adapter you have.

 

[johnklos]

I disagree with CelGen for two reasons. Drive vendors don't make new chipsets for each drive - they use chipsets which have already been made. There'd be no savings to cut out something which is essentially free. That is, all drives except HVD must already support single ended operation, so why would anyone specifically disable features that already exist? That wouldn't make sense. The second, and perhaps more compelling reason, is that while the electronics determine the physical bus configuration (LVD versus SE), drives begin the negotiation phase at the slowest speed, then negotiate higher speeds. So, in reality, I bet there isn't a SCSI drive in the world that couldn't be told to communicate at 5 MB/sec.

When you try to do anything with SCA drives, one must remember that SCA drives are all 16 bits wide, so to get them to see anything at all on a single ended bus, all 16 bits must be terminated properly. I've found the easiest way to do this is to have a full wide bus with a single ended wide terminator on one end, then connect the 8 bit Mac interface to a 16-bit-to-8-bit adapter on the other. Or, if possible, have two 16 bit SE terminators on each end and the wide-to-narrow adapter for the Mac's SCSI somewhere in the middle.

I have a number of 160 MB/sec Acard SCSI-IDE adapters which only work one of the two ways above, too. You can't get them to work at all if just 8 bits worth of the bus are terminated.

If your SCA adapter doesn't already have termination built-in, then you're going to have a hard time getting it to talk 8 bit.