Quantum 10K II - Manual (Page 314)

Feature Descriptions
Quantum Atlas 10K II Ultra 160/m SCSI Hard Disk Drives 6-13
NOTE
In a multimode environment, any insertion or removal that changes the bus
mode causes a transceiver mode change reset event.
System Considerations
It is not possible for the suppliers of various system components (e.g., targets,
initiators, backplanes, terminators) to guarantee that a system can operate under
“Hot Swap Case 4” conditions. Therefore, the system integrator bears the
responsibility for ensuring that the system can meet “Hot Swap Case 4” operational
criteria.
There are two metrics key to ensuring “Hot Swap Case 4” tolerance:
1. When a drive is being hot inserted into an active bus, a smaller capacitance on
the SCSI bus pins create a smaller (that is, a lesser charge) transient spike on
the bus.
2. When the drive is the closest drive to the connector at which another drive is
being hot inserted, it is desirable that the input receivers ignore short low
amplitude transients (usually via a low pass filter).
LVD SCSI devices may require more stringent system design to tolerate transients
that occur during Case 4 insertion or removal. System integrators should consider
the following when designing their backplanes or buses:
1. Larger connector-to-connector spacing causes the transients associated with hot
swapping to be attenuated dramatically before reaching an operating drive.
2. Larger SCSI signal-trace capacitance (that is, lower impedance) is preferable for
minimizing transient spikes, but can cause other bus problems unrelated to hot
swapping. Draft standard SCSI-3 SCSI SPI-2 (SCSI Parallel Interface), Revision
18, Section 6.6.2 illustrates the tradeoffs between trace capacitance and drive-to-
drive spacing.
3. The universe of drives needs to be homogeneous. A 15 pF drive hot-inserted into
a rack of 15 pF drives presents no difficulty. A 30 pF drive inserted into a rack of
10 pF drives with very close connector spacing, however, is more likely to cause
problems.