Dell TL2000 manual Physical Characteristics of the Scsi Interface, Using Multiple Scsi Buses

Maximum Bus Length Between Terminators (in

meters)

25

12 (LVD)

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).

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:

vThe SCSI bus is terminated properly at each end

vCable 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

Point-to-point (1 server and 1 drive)

Multi-drop/daisy-chain (1 server and multiple drives)

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: 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.

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 3-7