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Multi-Server Data Sharing
A host computer with a SCSI controller connected to a bus is a SCSI initiator. The Library is a
SCSI target. SCSI rules permit multiple initiators on a single bus. Therefore, with the proper
host software, it is possible to connect multiple hosts to a single Library over a single SCSI bus.
This allows multiple hosts to operate the library robotics, loading and unloading cartridges as
each host requires.
In a library system with many drives, it might be desirable to use multiple SCSI buses for the
drives so the data transfer rate of the drives is not limited by bus bandwidth. Individual drives
can be connected to separate hosts. Using special software, one of the hosts can act as a master
server, processing all robotics commands and permitting several hosts to share a common
database.
SCSI Configuration
The Library standard SCSI interface is a Fast/Wide LVD/SE using high-density, 68-pin D-series
connectors. For more information, see Appendix C, "Installation."
SCSI Bus Performance Considerations
Drives
With a standard Fast/Wide SCSI interface, each drive offers a sustained native data transfer rate
of 6 MB/s. In a two-drive unit, the total native rate is twice these rates. The rates for compressed
data are the native rates multiplied by the compression factor, which depends on file content, but
averages approximately 2:1.
Data Transfer Rate
The data transfer rate of the Library depends on the type of the AIT drive, number of drives, and
the number of drives connected to the SCSI bus. The library robotics imposes minimal loading
on the bus.
AIT-2
AIT-2
Each drive has a maximum sustained rate of 12 MB/s with compressed data. As a result, the
transfer rate of a two-drive unit occupies the full bandwidth of the bus. Sharing a SCSI bus
among more than two drives degrades the maximum performance of the library system.
Internal Cabling Configuration
Each SCSI bus in the Library is wired separately. The library robotics and drive 1 share one bus;
add-on drives are connected to separate SCSI buses. SCSI jumper cables are available to allow
the drives and robotics of a unit to be daisy-chained to a single SCSI bus. For more detailed
information, see Appendix C, "Installation."
Fast/Wide
Sustained
@ 40 MB/s (burst)
@ 6 MB/s (native)
@ 12 MB/s (compressed)
System Description 1-3
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Troubleshooting
