Technical data

Device Support on OpenVMS Systems
7.18 OpenVMS Alpha SCSI Port and Class Drivers
7.18 OpenVMS Alpha SCSI Port and Class Drivers
V6.2
The following sections describe OpenVMS Alpha SCSI class and port device
driver restrictions.
7.18.1 Add-On SCSI Adapters
V6.2
Version 6.2 and later of OpenVMS Alpha supports various add-on SCSI adapters.
Compaq’s AlphaGeneration platforms typically support one or more integral SCSI
adapters, with the option of installing additional add-on SCSI adapters. Due to
differences in device-naming conventions used between the Alpha console and
OpenVMS, the OpenVMS device name may not match the name displayed by the
console.
For example, the console designation for a SCSI device on the integral SCSI
adapter may be DKA100. However, when two additional add-on SCSI adapters
are added, the ‘‘A’’ designation becomes ‘‘C’’, and DKA100 appears as DKC100
when OpenVMS is running.
Note that although the console and OpenVMS device names may be different,
the unique specification of a device name from the console to the device name
under OpenVMS stays consistent, provided add-on SCSI adapters are not added
or removed.
7.18.2 SCSI Disk I/O Performance Degradation for KZMSA XMI and Adaptec
1742A Adapters
V6.2
As a result of the SCSI-2 Tagged Command Queuing (TCQ) support in OpenVMS
Alpha Version 6.2, Compaq has determined that customers with KZMSA XMI
to SCSI and Adaptec 1742A adapters may experience a 20% SCSI disk I/O
performance degradation because TCQ is not implemented for these adapters.
The performance degradation is in the area of increased CPU cost per I/O.
Customers running at less than maximum CPU utilization under OpenVMS
Alpha Version 6.1 may not experience any degradation under OpenVMS Alpha
Version 6.2.
Compaq does not expect this situation to significantly affect DEC 7000 customers
planning to upgrade to DEC 8000 Family systems using KZMSA adapters
because the speed of those processors should offset the performance degradation.
However, DEC 7000 customers who upgrade to OpenVMS Alpha Version 6.2 will
experience the SCSI I/O disk performance degradation.
Compaq expects that this will significantly affect existing DEC 2000 Model 300
systems customers that use the Adaptec 1742A SCSI adapter.
7.19 OpenVMS Alpha Device Support Documentation
As of OpenVMS Version 7.2, the Writing OpenVMS Alpha Device Drivers in
C manual no longer ships with the OpenVMS documentation set. The latest
revision of this manual is available from Digital Press. For more information, see
the following web site:
http://www.bh.com/digitalpress
7–12 Device Support on OpenVMS Systems