Mixed SCSI popuulation

[alphaa10]

I recently bought an Adaptec 39160-- a slightly more expensive, dual-channel SCSI for ultra 160 devices.

However, I have yet to install the controller, pending a clearer understanding of termination and compatibility issues.

The primary appeal of the 39160 was its fastest drive could run as fast as possible from channel A, while my other, slower devices could run from the same controller on channel B.

In addition to a single Fujitsu ultra 160 LVD device, I have four other, much slower IBM LVD devices, all of them the same model IBM 18gb DNES 318350-- a fast, wide "multimode" LVD/SE drive with an SCA interface.


Questions--


1. Use of an SCA/68-pin Adapter

A major consideration is the use of an adapter to connect the IBM devices' 80-pin SCA interface with the 68-pin connector on the LVD cable.

While it might seem simple to use four adapters for the IBMs, Adaptec has counseled against use of any adapter to convert the drive's native SCA 80-pin (hot swap) interface to 68-pin.

Other vendors have assured me they have no problems with using adapters, provided they are made with sufficient quality.

Have any forum members an opinion about adapters and their reliability? Any recommended vendors?


2. Proper termination

Since the 39160 is an LVD controller, proper termination is vital.

If adapters are OK, how should I terminate the IBMs? Is passive termination a viable option?

Active termination, while recommended by most experts, causes some terminated adapters to run noticeably hot. Although I plan to put all four IBMs in heavy ventilation, noticeable heat is something I want to avoid because it invites data catastrophes.

For that reason, I would like to bypass active termination altogether, but do not want any data issues.

Of the four drives on channel B, only one need be terminated if the adapter's channel B is also terminated (auto) at the adapter. Likewise for channel A, I presume.

I look forward to your comments and suggestions.

 

[alphaa10]

Additional information on the IBM LVD/SE Multi-mode model

Both 68-pin and 80-pin of LVD/SE Multi-mode models do not have any SCSI Terminator.

It is user responsibility to make sure that all required signals are adequately terminated at both ends of the bus cable.


Terminator Power

The 50-pin and 68-pin models supply terminator power to pin #26 of 50-pin connector and pin #17,18,51,52 of 68-pin connector through current limiter and shotky diode when jumper plug is set at position #G of J-6
jumper block.

For jumper setting, see 6.2, “Option Jumper Block” on page 28.
The 80-pin models do not supply terminator power.

 

[SomeJoe7777]

1. I've never had any problems with 68-pin/SCA adapters. However, the purpose of the adapter is to bring out the power connections to a molex connector, and also to bring out the SCSI ID selectors (usually as jumpers). Make sure that all SCSI IDs are set properly (unique for each device, remember that the host adapter uses an ID also, usually 7).

2. With LVD devices, active termination doesn't dissipate nearly as much power as it did when used with SE devices. There should be no problem using an active terminator, and in fact, I believe it's actually required for LVD devices.

Many LVD internal 68-pin cables have an active terminator already on the end of the cable (example). This is the best method for terminating an internal SCSI chain. This terminator gets its power from the bus itself, so you don't have to worry if any of the devices supply termination power to the bus or not. (Most LVD controllers supply the termination power to the bus themselves).

On a further note, many LVD controllers will run each device on the bus at its optimal speed. Thus, on an LVD bus, you can mix Ultra2 SCSI (80 MBps), Ultra160 SCSI (160 MBps), and Ultra320 SCSI (320 MBps) devices on the same bus, and the controller will talk to each at its native speed. In other words, the bus will not slow down to the slowest device if all devices are LVD. Adding one SE device will slow the entire bus down to SE speeds.

 

[alphaa10]

Many LVD internal 68-pin cables have an active terminator already on the end of the cable (example). This is the best method for terminating an internal SCSI chain. This terminator gets its power from the bus itself, so you don't have to worry if any of the devices supply termination power to the bus or not. (Most LVD controllers supply the termination power to the bus themselves).

On a further note, many LVD controllers will run each device on the bus at its optimal speed. Thus, on an LVD bus, you can mix Ultra2 SCSI (80 MBps), Ultra160 SCSI (160 MBps), and Ultra320 SCSI (320 MBps) devices on the same bus, and the controller will talk to each at its native speed. In other words, the bus will not slow down to the slowest device if all devices are LVD. Adding one SE device will slow the entire bus down to SE speeds.

Thanks very much-- I was very active the week of the original message on a number of other forums, and I apparently forgot to check back and thank you for your help. On placing an additional message this evening, I happened to check this thread, and found your reply. Sorry for the lennnnnnnngthy delay.

 

[alphaa10]

As it turned out, I had forgotten to indicate in member notification settings to send an email to me if anyone replied. Since no link from Tom's Hardware appeared in my inbox, I did not check directly.

(My notification of a response to any post is now set to ON.)