HP SW TL881 DLT Mini-Lib/1 Compaq TL881 MiniLibrary System Users Guide (May 19 - Page 63

SCSI Bus Performance Considerations, Drives, Internal Cabling Configuration, Bus Length Limitations

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Operation 2-37 SCSI Bus Performance Considerations The data transfer rate of the DLT MiniLibrary is dependent on the type of drives and on the SCSI bus configuration. The bandwidth of the SCSI bus is limited. Drives With a standard SCSI interface, modules equipped with the DLT20/40 series can provide a maximum sustained native transfer rate of 1.5 MB/second. With both drives operating, the DLT20/40 native transfer rate is 3.0 MB/second. The rates for compressed data are the native rates multiplied by the compression factor, which depends on file content, but averages approximately 1.7. Internal Cabling Configuration The differential MiniLibrary system is wired in an independent-bus SCSI configuration: the robotics and each of the drives has its own SCSI bus. SCSI jumpers are available for those applications requiring that some combination of drives and robotics are daisy-chained to a single SCSI bus. The single-ended table-top unit has the robotics and first DLT drive daisychained internally to shorten the total internal cable length. The second drive is on an independent bus. Bus Length Limitations The single-ended SCSI-2 bus is limited to 6 meters in length, and the singleended Fast SCSI-2 bus is limited to 3 meters overall length. In contrast, differential SCSI-2 and Fast SCSI-2 buses may be up to 25 meters long. Physical Configuration All modules in a MiniLibrary system must be mounted in a rack except for the table top module version. When a system is ordered, all the modules are supplied in a rack-mount configuration. Modules cannot be operated alone except for the MiniLibrary Base Module, which can be converted to operate as a free-standing 10-slot library.

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Operation
2-37
SCSI Bus Performance Considerations
The data transfer rate of the DLT MiniLibrary is dependent on the type of
drives and on the SCSI bus configuration. The bandwidth of the SCSI bus is
limited.
Drives
With a standard SCSI interface, modules equipped with the DLT20/40 series
can provide a maximum sustained native transfer rate of 1.5 MB/second. With
both drives operating, the DLT20/40 native transfer rate is 3.0 MB/second.
The rates for compressed data are the native rates multiplied by the
compression factor, which depends on file content, but averages
approximately 1.7.
Internal Cabling Configuration
The differential MiniLibrary system is wired in an independent-bus SCSI
configuration: the robotics and each of the drives has its own SCSI bus. SCSI
jumpers are available for those applications requiring that some combination
of drives and robotics are daisy-chained to a single SCSI bus.
The single-ended table-top unit has the robotics and first DLT drive daisy-
chained internally to shorten the total internal cable length. The second drive is
on an independent bus.
Bus Length Limitations
The single-ended SCSI-2 bus is limited to 6 meters in length, and the single-
ended Fast SCSI-2 bus is limited to 3 meters overall length. In contrast,
differential SCSI-2 and Fast SCSI-2 buses may be up to 25 meters long.
Physical Configuration
All modules in a MiniLibrary system must be mounted in a rack except for the
table top module version. When a system is ordered, all the modules are
supplied in a rack-mount configuration. Modules cannot be operated alone
except for the MiniLibrary Base Module, which can be converted to operate as
a free-standing 10-slot library.