HP 3000 Manuals HP 3000 Manuals
Chapter 2 Peripherals
Fast/Wide (Differential) SCSI Support
by Wendell Griggs
Commercial Systems Division
Support for the HP-PB High-Performance Fast/Wide SCSI adapter and
half-height 3.5-inch 2.0 GB Fast/Wide (Differential) SCSI disks are
included in this release of MPE/iX on HP 3000 Series 9x7, 9x8, and
Corporate Business Systems (99x).
Features And Benefits
Following is a summary of the major features and benefits of the
Fast/Wide SCSI adapter (P/N 28696A) and in some instances a comparison to
the Single-Ended SCSI adapter (P/N 28642A):
* Host Performance. The number of processor interrupts issued by
the adapter for any particular I/O is significantly less than that
of the Single-Ended adapter. This is due to the Fast/Wide SCSI
adapter's ability to manage any I/O through the entire SCSI
transaction without assistance from host software. The Fast/Wide
SCSI adapter also achieves a much higher rate of I/O concurrency,
augmenting efficiencies obtained from the use of SCSI command
queuing by host software. The result is much more efficient use
of host CPU resources when launching I/O's to the adapter and
completing I/O's as signaled by interrupts from the adapter.
* Increased Connectivity. The Fast/Wide SCSI bus allows for the
connection of up to 15 devices. However, like an I/O interface
channel configuration, performance parameters must be considered
carefully when determining the appropriate number of devices for
connection to a single channel.
As with the Single-Ended SCSI adapter, the Fast/Wide SCSI adapter
is always set to SCSI bus address (or SCSI Target ID) 7. The
priority of devices arbitrating for use of the SCSI bus is
determined by the SCSI Target ID. The IDs in descending priority
order are 7, 6, 5, 4, 3, 2, 1, 0, 15, 14, 13, 12, 11, 10, 9, and
8.
* Increased Channel Capacity. The burst transfer rate of the
Fast/Wide SCSI bus (20 Mbytes per second) is achieved via the Wide
Data Transfer mode (16 bits plus 2 parity) in conjunction with a
decreased transfer period. Enhancements in the interface hardware
provide additional efficiencies on both the host adapter and
device side of the SCSI connection.
* Increased Cabling. The electrical characteristics of the
Fast/Wide (Differential) SCSI bus support a maximum cable length
of 25 meters (total distance from connector on the adapter to the
terminator at the end of the bus, including cabling within
peripheral enclosures); which is an increase of 19 meters over the
limit imposed by the Single-Ended SCSI bus.
The 2.0 Gbyte Fast/Wide (Differential) SCSI disks also offer a number of
advantages over the currently and previously available Single-Ended SCSI
disk mechanisms:
* Decreased average seek and rotational latency times
* Higher external data transfer rates (Host/Controller while in Wide
Synchronous mode at 20 Mbytes per second)
* Improved reliability with Mean Time Between Failures (MTBF) of
500,000 hours
* Decreased power consumption during drive startup, run, and seek
operations.
MPE/iX software support includes use of a Fast/Wide SCSI disk as a boot
device (LDEV 1) in addition to system and non-system volumes. Mirror
Disk configurations of Fast/Wide SCSI disks are also supported. Device
specific host software enhancements allow for greater I/O concurrency via
the use of SCSI Command Queuing, thus allowing up to 8 active I/O's per
device.
For ordering and configuration information, contact your sales
representative.