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Restrictions
The following restrictions apply when using the VAX SCSI option in certain
systems. Please adhere to the restrictions below in order to ensure correct
operation:
Model Restriction
5140-V1 Takes up DSH42 (async option) Slot
Cannot be used with the KZQSA
5140-V2 Takes up Turbo-channel adapter slot
5140-V3 Cannot be used with KZQSA
5140-V4 Takes up DSH42 (Async option) Slot
Cannot be used with the KZQSA
5140-V5 TBD
Performance
Compaq’s VAX SCSI adapters bring state of the art Ultra SCSI disks and
tapes to the VAX architecture, and significantly increase the I/O throughput
available.
For single block, sequential I/O (512 bytes) the Compaq adapters are capable
of doing 5000 I/Os per second, running OpenVMS to Ultra SCSI disks.
Large I/O throughput is limited more by the CDAL architecture than by
SCSI. Sequential I/Os of 127 blocks (65024 bytes) achive 10.3Mbytes/sec.
For comparison, large sequential reads over DSSI achive 3.3MBytes/sec, and
the native narrow SCSI (onboard) achives 3.0Mbytes/sec in equivalent tests.
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