Installation guide

Glossary
Manual No. 775007 G-11
Ultra SCSI
Ultra SCSI, or Fast 20 SCSI is a high performance SCSI protocol that has a
bus speed of 20 MegaBytes per second in the Narrow SCSI configuration
and 40 MegaBytes in the Wide SCSI (Fast 20 Wide SCSI) configuration.
Ultra2 SCSI
Ultra2 SCSI, or Fast 40 SCSI is a higher performance SCSI protocol than
Ultra SCSI. Ultra2 SCSI has a bus speed of 40 MegaBytes per second in the
Narrow SCSI configuration and 80 MegaBytes in the Wide SCSI (Wide
Ultra2 SCSI) configuration.
Write-Back Cache
Refers to a caching strategy whereby write operations result in a completion
signal being sent to the host operating system as soon as the cache (not the
disk drive) receives the data to be written. The target SCSI drive will receive
the data at a more appropriate time, in order to increase controller
performance. An optional cache battery backup can be used to protect
against data loss as a result of a power failure or system crash.
Write Through Cache
Refers to a caching strategy whereby data is written to the SCSI drive before
a completion status is returned to the host operating system. This caching
strategy is considered more secure, since a power failure will be less likely to
cause loss of data. However, a write through cache results in a slightly lower
performance.