HP StoreEver Ultrium Tape Drives - Manual (Page 69)

A SCSI configuration guide
SCSI in HP StorageWorks Ultrium devices
HP StorageWorks Ultrium 1760 and 920 tape drives are high performance Ultra320 SCSI compatible
devices; HP StorageWorks Ultrium 448 and 232 tape drives are high performance Ultra160 SCSI
compatible devices.
They are designed to operate on a low voltage differential (LVD) SCSI interface and are not compatible
with high voltage differential (HVD) SCSI devices.
Ultrium 1760 and 920 tape drives support a burst transfer rate of 320 MB/sec; Ultrium 448 and 232
tape 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 Ultra320 bus for HP Ultrium 1760 and 920 tape drives. An Ultra160 or Ultra320 bus for HP
Ultrium 448 and 232 tape drives.
If you attach the drive to a lower specification SCSI bus, it will still work but data may not be
transferred as quickly. Ultra2 SCSI is also supported, but performance may be degraded.
• 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.
Daisy chaining devices
NOTE:
We do not recommend daisy chaining the HP StorageWorks Ultrium 1760 and 920 tape drive with
other devices.
If you need to connect multiple devices to the bus, performance may be restricted if there are too many
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. HP recommends that you do not attach
the tape drive to the same SCSI bus as the disk drive. See “ SCSI termination ” on page 71 for more
information about terminating HP StorageWorks Ultrium 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).
Ultrium Half-Height SCSI Tape Drives 69