HP StoreEver DAT Tape Drives - Manual (Page 62)

SCSI configuration guide 62
Removable drives
For HP StorageWorks DAT removable tape drives, termination is provided by connecting a
terminator to the spare SCSI connector on the rear of the tape array. There are two connectors for
each bay in the tape array. It doesn't matter which is used for SCSI-IN and SCSI-OUT.
If you have each removable drive in the tape array attached to a separate bus, then, for each bay in
use, you must attach a terminator to the spare connector for each device.
If you are using the removable drives to mirror backups, you can daisy-chain devices (but no more
than two on each SCSI bus). Connect an LVD-rated cable from the spare SCSI connector for the first
device to one of the SCSI connectors for the second device and attach the terminator to the spare
SCSI connector for the second device.
Refer to your tape array documentation for detailed instructions.
SCSI cables
Cables matter in SCSI systems. There are two factors to consider: cable length and cable quality.
Cable length
• For single-ended SCSI with Fast devices there is a maximum permissible length of 6 meters for a
single SCSI bus.
• For single-ended SCSI with Ultra devices the maximum permissible length is 3 meters for four or
fewer devices, and 1.5 meters for more than four devices.
• For LVD SCSI the maximum length for a single device is 25 meters. For multiple devices, the
maximum combined internal/external length is 12 meters.
• If you have a combination of LVD and SE devices on the bus, the maximum cable length reverts
to the SE specification. See note on SE and LVD interfaces for more information.
• For best performance, keep lengths to a minimum, but avoid very short overall lengths (less than
0.5 meters).
Cable quality
• It is important to use good quality cables. Generally speaking, cable quality affects performance
and reliability. This is particularly true for external, shielded cables.
• Look after your SCSI cables. In particular, take care when connecting or disconnecting not to
damage the high-density connectors. Avoid putting excessive twists in external shielded cables,
as this can cause premature failure.
With internal devices
For HP StorageWorks DAT internal devices, you need a SCSI ribbon cable with the correct
termination. HP StorageWorks DAT 72 drives have a 68-pin wide, high-density SCSI connector. A
suitable cable is supplied with the tape drive. If you are using an HP StorageWorks DAT drive on an
internal bus with other peripherals that run at Ultra160 speeds, it is important that a 68-pin
LVD-compatible ribbon cable is used. Do not connect your tape drive to lower-rated SCSI or to
narrow SCSI.