The Scsi Bus And This Jukebox; Mixing Wide And Narrow Devices - HP Surestore 80ex - Optical Jukebox User Manual

Operating This Jukebox on a SCSI Bus

The SCSI Bus and This Jukebox

The SCSI Bus and This Jukebox
This jukebox is a "fast and narrow" SCSI device that uses a single-ended SCSI bus.
This jukebox does not support logical unit number (LUN) addressing.
When considering adding other peripherals to the jukebox bus, you should 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?
Before addressing some questions involved in deciding whether to place another
device on the jukebox bus, we can say that, as a general rule, HP recommends that
the jukebox be the only device on a bus. The more devices on the bus, the more
chance for problems. Performance of one or all of the devices on the bus can be
affected.
If you are still considering adding a device, you might first consider the quantity of
data that the bus will have to carry, the frequency of data transfer, and the priority of
this data transfer in your business. If you are using the jukebox 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 are more random in both frequency and
data size. If you expect to be using the jukebox in the same time-frame as the other
device, or devices, this might indicate that you may experience a drop in
performance.

Mixing Wide and Narrow Devices

An a preliminary note to this discussion, HP highly recommends 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 would be lost if the devices were set up as depicted in
the figure below.
B-6 Appendix B