Adding Devices To The Bus - HP SureStore Optical Jukebox 160ex Service Manual

Theory of Operation
Configuring This Jukebox on a SCSI Bus

Adding Devices to the Bus

When considering adding other devices to the jukebox bus, consider the
following:
• Will adding a device onto a bus with this jukebox interfere or degrade
the performance of the jukebox or the device that is added?
• If the decision is made to add other devices to the jukebox bus, what
SCSI requirements must be observed to make sure the bus will work?
The recommended configuration of this jukebox is as the only device on a
bus. The recommendation is the same whether the bus is single-ended or
differential. One reason for the recommendation is that interactions on a
SCSI bus can be complicated. The more devices on the bus, the more
chance for problems. Another reason is that this jukebox, when fully
utilized, is capable of using up the full bandwidth of the bus.
Performance of one or all of the devices on the bus can be affected.
Consider the quantity of data that the bus will have to carry, the
frequency of data transfer, and the priority of the data transfer under
consideration. If the jukebox is used as a backup or archive device, the
demands on the jukebox will be different than if the jukebox is used for
near-online storage where requests for data are more random in both
frequency and amount. If the jukebox will be used at the same time as
the other device, or devices, you should expect a drop in performance.
Mixing Wide and Narrow Devices
Try to cable systems so that you do NOT mix wide and narrow buses.
Connecting devices of the same bus width, such as all narrow (50-pin) is
a simple process of daisy-chaining the devices, and terminating both
ends of the bus. However, mixing narrow and wide devices invites
problems.
This method should only be implemented by an experienced systems
integrator who is highly knowledgeable about SCSI. Since the wide
(68-pin) buses need more data lines on the bus for their data transfer, it's
necessary that the cables connecting the devices are 68 pin. The data
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