Software Installation and User’s Guide167ICP RAID NavigatorSynchronous Transfer and Synchronous Transfer RateDifferent from the older asynchronous transfer mode, synchronous transfer offers highertransfer rates on the SCSI bus. The maximum synchronous data transfer rate depends onthe width of the SCSI bus (8 bit narrow SCSI, 16 bit wide SCSI) and the frequency of thesignals on the SCSI bus (10 MHz for Fast SCSI, 20 MHz for Ultra SCSI and 40 MHz forUltra2 SCSI and Ultra160/320 SCSI). The maximum data transfer rates are shown inTable 11-17.Note: The maximum synchronous data transfer rate between a SCSI device and the ICP RAIDcontroller can be limited. This limitation may become necessary if a particular SCSIcabling does not allow the maximum rate the controller and the drive could achieve.Adjust the synchronous transfer rate in the SCSI parameters / Initialize menu.Note: To select a transfer rate above 10 MB/s the protocol must be set to SCSI-III. Higherfrequencies (single ended SCSI) require better cabling, shorter cables and a professionaltermination of the SCSI bus.Domain ValidationDomain Validation is a cyclical check of the correct data transfer at agiven rate for ICP RAID controllers with Ultra160 SCSI channels.Normally this parameter is Off.DisconnectThis SCSI feature enables a SCSI device to disconnect from the SCSI bus. By releasingthe SCSI bus while the device doesn’t need it, the bus becomes free for other devices totransfer or receive data. An example of a disconnect situation is a hard disk that needstime to read data from its media after receiving a read command. It may then disconnectfrom the SCSI bus so that other devices can transfer data. Later on it reconnects when it isable to deliver the data instantly. You can change the disconnect setting for a hard disk inthe SCSI parameters / Initialize menu.Table 11-17. Data Transfer RatesNarrow SCSI(8Bit)Wide SCSI(16Bit)Fast SCSI 10 MB/s 20 MB/sUltra SCSI 20 MB/s 40 MB/sUltra2 SCSI - 80 MB/s †Ultra160 - 160 MB/s †Ultra320 - 320 MB/s †† (LVD SCSI (low voltage differential) only)
