Compaq StorageWorks TL881/TL891 Family MiniLibrary System Reference Guide (July 2000)

System Description
1-7
Compaq Confidential – Need to Know Required
Writer:
Bob Young
Project:
Compaq StorageWorks TL881/TL891 Family MiniLibrary System Reference Guide
Comments:
Part Number:
127510-002
File Name:
b-ch1 System Description.doc
Last Saved On:
7/12/00 10:42 AM
SCSI Interface Configurations
DLT drives in TL891 MiniLibraries use either a fast-wide High Voltage
Differential (HVD) or a fast-wide, single-ended SCSI interface. The choice
must be made at the time of purchase. DLT drives in a TL891 MiniLibrary
system use a fast-wide HVD SCSI interface. DLT drives in a TL891DLX
MiniLibrary use a fast-wide auto-sensing Low Voltage Differential
(LVD)/single-ended SCSI interface.
SCSI Bus Performance Considerations
Data Transfer Rate
The data transfer rate of the MiniLibrary is dependent on the type and number
of drives and on the SCSI bus configuration. The bandwidth of the SCSI bus is
limited. As a result, the transfer rate of DLT drives can be limited by sharing a
SCSI bus with another tape or disk drive. It is recommended that the
MiniLibrary be installed on its own controller for optimum performance.
Drives
With a standard SCSI interface, modules equipped with DLT 20/40 drives
have a native data transfer rate of 1.5 MB/s; 3.0 MB/s for two drives. Modules
equipped with DLT 35/70 drives have a native data transfer rate of
5 MB/s; 10 MB/s for two drives. Modules equipped with DLT 40/80 drives
have a native data transfer rate of 6 MB/s; 12 MB/s for two drives. The rates
for compressed data are dependent on compression ratio, record size, data
type, and other system parameters, but average 1.7 times greater than the
native rate.
Internal Cabling Configuration
The differential and Low Voltage Differential (LVD) versions of the
MiniLibrary Base Module are wired in an independent-bus SCSI
configuration. That is, 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 can be daisy-chained to a single SCSI bus.
The single-ended table-top version, however, has the first drive daisy-chained
internally to the robotics in order to reduce cable length. These configurations
are described in more detail in Chapter 3, “Installation.”