Compaq 4200 Family - Manual (Page 15)

Introducing the Enclosure 1–3
SCSI Buses
The enclosure supports only Wide-Ultra2 SCSI, wide (16-bit), internal LVD buses.
Depending on the host interface, the external SCSI bus, the bus from the I/O module to the
host can be either Wide-Ultra or Wide-Ultra2, LVD or SE. The SCSI bus type determines
the length of this bus, and therefore, the maximum cable length. The standard Compaq
cable length of 12 ft (3.7 m) ensures satisfactory operation. As for all SCSI buses, the
shorter the cable, the more efficient the bus operation.
High Availability
The high availability features of the enclosure are a function of the fans and the power
supplies.
Variable Speed Fans
All enclosures have two variable speed fans. In all configurations, the failure of one fan
automatically causes the other fan to operate at a high speed. This ensures that the failure
of a single fan does not disable the enclosure.
Power Supplies
In a single power supply configuration, the failure of a power supply disables the
enclosure. Use the optional redundant power supply configuration to prevent this. In this
configuration, the failure of a single power supply or fan does not disable the enclosure.
Data Integrity
Data integrity could be compromised if data transfers occur when there is no DC power to
the I/O module or the drives, To avoid inducing errors, the power pins on these elements
are longer than the data pins. This ensures that power is always present when a data
transfer occurs.