IBM System Storage TS3100, Руководство по установке, эксплуатации и обслуживанию

Страница: 63 / 375

Any combination of up to two initiators (servers) and up to four targets (devices)
is allowed on a single SCSI bus if the following conditions are met:
v
The SCSI bus is terminated properly at each end
v Cable restrictions are followed according to the SCSI-3 specification
Under the SCSI-3 protocol, this type of attachment allows cable lengths of up to 25
m (81 ft) with the appropriate cable and terminator. The table below gives the
maximum bus length between terminators for the LVD interface. For information
about cable connectors, see “SCSI Connectors and Adapters” on page 3-10.
Table 3-2. Maximum bus length between terminators
Type of Interconnection
Maximum Bus Length Between Terminators (in
meters)
Point-to-point (1 server and 1 drive) 25
Multi-drop/daisy-chain (1 server and
multiple drives)
12 (LVD)
Note: The maximum bus lengths stated in this table include the internal length of the bus.
For maximum performance, multiple SCSI buses may be required (see “Using
Multiple SCSI Buses”), and IBM Ultrium Tape Drives must be the only target
devices that are active on the bus.
Note: Daisy-chaining is NOT recommended due to potential issues with SCSI bus
performance, SCSI cables/connectors, and host bus adapters.
Note: For maximum performance, the quantity of tape drives that you can attach
to one SCSI bus is limited, and is based on the type of bus that you have
and the amount of data compression achieved. Ultra160 SCSI buses have a
bandwidth of 160 MB per second. The table below lists the types of SCSI
buses and gives the recommended maximum quantity of drives that you can
attach.
Table 3-3. Recommended maximum quantity of drives per SCSI bus
Type of Drive Ultra 160 SCSI Bus
LVD Ultrium 3 1 drive at 2:1 compression
Using Multiple SCSI Buses
The library has two SCSI connectors for each tape drive in the library. Each drive
can be daisy-chained using a SCSI bus jumper.
Note: Daisy-chaining is NOT recommended due to potential issues with SCSI bus
performance, SCSI cables/connectors, and host bus adapters.
Removal of any jumpers will create a SCSI bus for each drive installed in your
library for attachment to multiple servers or to multiple SCSI adapter cards on one
server. Remember that each SCSI bus must be terminated. Multiple SCSI buses
may be required for maximum performance, depending on the application and
data compression ratio. Note, however, that library (Medium Changer) control is
required on at least one SCSI bus.
Chapter 3. Installation Planning
3-9