HP StoreEver DAT Tape Drives - Manual (Page 63)

13 SCSI configuration guide
SCSI in HP StorageWorks DAT devices
HP StorageWorks DAT tape drives are Ultra160 SCSI-2 compatible devices. They are designed to
operate on a low voltage differential (LVD) SCSI interface. They are 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 “ SCSI termination ” on page 65 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 (8-Bit or 16-Bit).
• The voltage level of the interface, which may be single-ended (SE) or low voltage differential (LVD).
HP StorageWorks DAT drives are Ultra 160 SCSI devices designed to operate on a low voltage
differential SCSI interface.
DAT SCSI Tape Drives 63