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

HP StorageWorks DAT Tape Drives User Guide 63
With external devices
The cable provided with all HP StorageWorks DAT external tape drives and autoloaders will attach
to a computer with a wide, very high density (VHD), LVDS SCSI connector.
If your server or host bus adapter is equipped with a high density (HD) wide SCSI connector, you
will need to order a 68-pin VHD-to-HD converter or 68-pin VHD-to-HD cable. See
www.hp.com/go/connect
.
With removable devices
For HP StorageWorks DAT removable tape drives, appropriate cables and terminators are provided
with the tape array.
Note on SE and LVD interfaces
SE and LVD define how the signals are transmitted along the cable.
• With single-ended (SE) SCSI, each signal travels over a single wire and each signal's value is
determined by comparing the signal to a paired ground wire. Signal quality tends to decrease
over longer cable lengths or at increased signal speed.
• With low voltage differential (LVD) signaling, signals travel along two wires and the difference in
voltage between the wire pairs determines the signal value. This enables faster data rates and
longer cabling with less susceptibility to noise than SE signaling and reduced power
consumption.
If you use LVD SCSI devices on the same bus as single-ended devices this will switch the LVD SCSI
host adapter into single-ended mode and restrict cable length.
If you connect only LVD SCSI devices, the bus will operate in low voltage differential mode and
Ultra160 speeds will be enabled. You can use a combination of Ultra160 and Ultra2 devices. Each
device will operate at its optimum speed.