HP StorageWorks DAT Tape Drives User Guide - SCSI (April 2005)

HP StorageWorks DAT Tape Drives User Guide 59
If none of these is available to you, try the following sources of information:
• The details of all installed devices and settings may have been written down and stored with
your computer's documentation (for new computers, this is often done by the supplier).
• Your HBA's documentation should tell you which settings it uses.
• Look at each device to find out its ID. This is usually easy with external devices. With internal
devices, you will probably need the help of the device's documentation to identify the SCSI ID
setting, which is usually set with jumpers.
Setting the SCSI id on HP StorageWorks DAT drives
For all cases, see the User Guide that came with your tape drive for more details. Note that host
adapters check SCSI IDs only at power-on, so any changes will not take effect until the host system is
power-cycled.
• On internal HP StorageWorks drives, set the SCSI ID by attaching or removing jumpers at the
rear of the drive, see ”Check the drive’s SCSI ID” on page 15.
• On external HP StorageWorks drives, the ID is displayed on the rear panel and can be set by
pressing the little buttons above and below the number (using a ball point pen), see ”Check the
drive’s SCSI ID” on page 25.
• On removable HP StorageWorks drives, the ID is set on the back of the tape array, see ”Set the
drive’s SCSI ID” on page 31.
SCSI termination
Terminators are essential, as they provide the correct voltages on the SCSI bus and prevent
unwanted signal reflections from interfering with data transfers. The rule is:
• There must be termination at both physical ends of the bus and only at the ends.
There are two main types of termination, active and passive. Active terminators reduce interference
and allow faster data throughput. On devices with high transfer speeds, such as HP StorageWorks
DAT 72 devices, active termination is required, using an LVD or multimode active terminator.
(Multimode terminators allow both LVD and single-ended devices to be connected to the same bus.
They detect the type of bus and automatically supply the correct termination. The terminator
supplied with HP StorageWorks DAT72 tape drives in LVD only. Multimode terminators may be used
instead.)
Normally the HBA forms one end of the SCSI bus and provides termination. You only need to ensure
that the other end of the bus is terminated.