CyberstormPPC SCSI issue with CD-Rom Drive - Page 2

Jope · 19 September 2014, 08:15

IMO it's a good practice to keep the bus at full width from the HBA to the last terminator, then adapt it at each device if you want to plug in narrow devices. This basically means that if you have one or more external scsi boxes, you should have wide boxes and put passive 68->50 adapters in them for the devices. Or just keep it all internal if you have enough space in your case.

As far as I have understood it, mixing wide + narrow on the same bus does not slow down the wide devices, UNLESS you do the upper bit termination + narrow conversion at some point and then connect the wide devices to the narrow side of your bus.

And like you have figured out there, if you decide to go for the option of converting the end of the bus to narrow, the adapter at that point must be of the upper bit terminating kind. Most of the cheap SCSI adapters you can buy just leave the unused bits floating.

Ami_GFX · 08 October 2014, 00:50

I just added a wide 68 pin scsi drive to my A4000. I can confirm that wide and narrow devices can coexist. The configuration I have now is a 3 device 68 pin scsi cable inside the Amiga. The center connector is connected to the Cyberstorm PPC scsi port. One side goes to the 68 pin drive. Active termination is enabled. The other side goes to a 68 pin to 50 pin adapter with termination. The 50 pin side of the adapter is connected to and external scsi port and I have a 250mb zip drive and a 2gb jaz drive connected to the external port in that order. The jaz drive is the last drive because it has better termination. I have active termination on both ends of the chain. Both the internal drive and jaz drive supply termination power and there is no problem if both are on at once.

I have an IDE DVDRW drive connected in slave mode to the IDE port with no master. This makes the Amiga boot faster because if I set the DVD drive to master, the Amiga trys to boot from it when it is switched on and it takes 30 seconds or so before it trys the scsi drive. My DVDRW drive is only 7 inches long which gives the PSU fan lots of clearance. The shortest scsi DVD or CD drive I've found is 7.6 inches long and most are longer. It also is a 50 pin drive. There are 68 pin scsi DVD drives but I haven't found one that is less than 8 inches. The 68 pin cables are much slenderer than the 50 pin cables and I am trying to create as much free space as possible inside the A4000D chassis so air can be moved around and keep my Cyberstorm PPC properly cooled. That means smaller drives with smaller cables.

alexh · 08 October 2014, 14:13

I thought we knew they could co-exist but didn't know if doing so had an impact on the maximum bandwidth to Ultra Wide devices?

Ami_GFX · 08 October 2014, 14:47

I should have put in that the bandwidth is normal on the wide drive. Around 14mb/s. On the narrow side I get up 7.3mb/s on the Jaz drive.

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19 September 2014, 08:15	#21
Jope - Join Date: Jul 2003 Location: Helsinki / Finland Age: 43 Posts: 9,861	IMO it's a good practice to keep the bus at full width from the HBA to the last terminator, then adapt it at each device if you want to plug in narrow devices. This basically means that if you have one or more external scsi boxes, you should have wide boxes and put passive 68->50 adapters in them for the devices. Or just keep it all internal if you have enough space in your case. As far as I have understood it, mixing wide + narrow on the same bus does not slow down the wide devices, UNLESS you do the upper bit termination + narrow conversion at some point and then connect the wide devices to the narrow side of your bus. And like you have figured out there, if you decide to go for the option of converting the end of the bus to narrow, the adapter at that point must be of the upper bit terminating kind. Most of the cheap SCSI adapters you can buy just leave the unused bits floating.

08 October 2014, 00:50	#22
Ami_GFX Registered User Join Date: Sep 2011 Location: USA North America Posts: 211	I just added a wide 68 pin scsi drive to my A4000. I can confirm that wide and narrow devices can coexist. The configuration I have now is a 3 device 68 pin scsi cable inside the Amiga. The center connector is connected to the Cyberstorm PPC scsi port. One side goes to the 68 pin drive. Active termination is enabled. The other side goes to a 68 pin to 50 pin adapter with termination. The 50 pin side of the adapter is connected to and external scsi port and I have a 250mb zip drive and a 2gb jaz drive connected to the external port in that order. The jaz drive is the last drive because it has better termination. I have active termination on both ends of the chain. Both the internal drive and jaz drive supply termination power and there is no problem if both are on at once. I have an IDE DVDRW drive connected in slave mode to the IDE port with no master. This makes the Amiga boot faster because if I set the DVD drive to master, the Amiga trys to boot from it when it is switched on and it takes 30 seconds or so before it trys the scsi drive. My DVDRW drive is only 7 inches long which gives the PSU fan lots of clearance. The shortest scsi DVD or CD drive I've found is 7.6 inches long and most are longer. It also is a 50 pin drive. There are 68 pin scsi DVD drives but I haven't found one that is less than 8 inches. The 68 pin cables are much slenderer than the 50 pin cables and I am trying to create as much free space as possible inside the A4000D chassis so air can be moved around and keep my Cyberstorm PPC properly cooled. That means smaller drives with smaller cables.

08 October 2014, 14:13	#23
alexh Thalion Webshrine Join Date: Jan 2004 Location: Oxford Posts: 14,331	I thought we knew they could co-exist but didn't know if doing so had an impact on the maximum bandwidth to Ultra Wide devices?

08 October 2014, 14:47	#24
Ami_GFX Registered User Join Date: Sep 2011 Location: USA North America Posts: 211	I should have put in that the bandwidth is normal on the wide drive. Around 14mb/s. On the narrow side I get up 7.3mb/s on the Jaz drive.

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