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

HP StorageWorks DAT Tape Drives User Guide 57
A SCSI configuration guide
SCSI in HP StorageWorks DAT devices
The HP StorageWorks DAT 72 tape drive is an Ultra160 SCSI-2 compatible device. It is designed to
operate on a low voltage differential (LVD) SCSI interface. It is not compatible with high voltage
differential (HVD) SCSI devices.
The drives support a burst transfer rate of 160 MB/sec. To benefit from this level of performance, it
is important to ensure that the drives are connected to a SCSI bus of a similar or higher
specification. This means that you need:
• An Ultra160 or Ultra320 SCSI host bus adapter. Ultra2 SCSI is also supported, but performance
may be degraded if there are several devices on the SCSI bus.
• LVD-rated SCSI cabling and terminators. The LVD interface enables the data to be transferred at
the drive's maximum rate and provides a maximum cable length of 12 meters.
We also recommend that the tape drive is connected to a dedicated host bus adapter. If you need
to connect multiple devices to the bus, performance may be restricted if there are too many (3 or
more) devices on the bus that are accessed simultaneously. Connecting devices of lower SCSI
specification, such as Ultra2 or Ultra SCSI, may also restrict performance to your tape drive. Using
Single Ended 8-Bit SCSI devices on the same bus is not recommended, as performance will be
severely impacted and complicated bus configuration is required to overcome bus termination
issues.
Make sure that the last device on the SCSI bus is terminated. We recommend that you do not attach
the tape drive to the same SCSI bus as the disk drive. See the section on SCSI termination for more
information about terminating HP StorageWorks DAT tape drives.
SCSI terminology
SCSI is a bus interface: all the devices are connected to a single cable (some of this may be inside
and some outside the host computer's case). The connection to the host itself is known as the Host
Bus Adapter (HBA). You can have several HBAs in a single computer, each with its own SCSI bus:
this is a common arrangement in high-performance servers. Some host bus adapters (such as the LSI
Logic LSI22320-R) have more than one SCSI bus available on a single card.
Various terms are used when describing SCSI devices. These terms relate to the factors that affect
performance and cable length:
• The speed of the data bus, which may be Fast, Ultra, Ultra2, Ultra3, Ultra160 or Ultra320.
• The width of the data bus, which may be Narrow or Wide (16-Bit or 8-Bit).
• The voltage level of the interface, which may be single-ended (SE) or low voltage differential
(LVD).
HP StorageWorks DAT 72 drives are Ultra 160 SCSI devices designed to operate on a low voltage
differential SCSI interface.