Dell PowerVault TL4000 - Manual (Page 50)

Note: For maximum performance, it is recommended to have a maximum of
one drive per SCSI bus.
– Only use the maximum system-to-device cable length of 25 m (82 ft) when
attaching directly to one device (a point to point interconnection).
Note: Daisy-chaining is NOT recommended due to potential issues with SCSI
bus performance, SCSI cables/connectors, and host bus adapters.
Physical Characteristics of the SCSI Interface
The library operates as a set of SCSI-3 devices. The Ultrium Tape Drives attach to
servers using an LVD Ultra160 SCSI interface. Each SCSI drive sled uses shielded,
HD68-pin connectors, and can attach directly to a 2-byte-wide SCSI cable.
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.
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 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.
3-8 Dell PowerVault TL2000 Tape Library and TL4000 Tape Library User's Guide