Specifications

SCSI configuration
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SCSI configuration
contents of this section
SCSI in hp surestore dat devices
what is SCSI?
the standards
setting up the SCSI bus
SCSI ID numbers
identifying SCSI IDs
setting the SCSI ID on hp surestore dat drives
SCSI termination
internal drives
external drives
removable drives
SCSI cables
cable length
cable quality
with internal drives
with external drives
with removable drives
VHD connectors
note on SE and LVD interfaces
scsi in hp surestore dat devices
The HP Surestore DAT 40 drive and HP Surestore DAT 40x6 autoloader are
ultra wide, 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 SCSI devices.
The drives support a burst transfer rate of 40 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 Ultra Wide, Ultra2 Wide, Ultra160 or Ultra3 SCSI host bus
adapter. Ultra Wide SCSI supports the maximum bus speed of 40 MB
per second, Ultra2, Ultra160 and Ultra3 SCSI exceed this.
● 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.
The HP Surestore DAT 24 drive and HP Surestore DAT 24x6 autoloader are
single-ended, fast SCSI-2 compatible devices. The drives support a burst
transfer rate of 20 MB/sec and should be used with a SCSI bus that meets the
Fast specification or higher. They are not compatible with high voltage
differential SCSI devices.
All HP Surestore DAT drives can be used with both LVD and single-ended host
bus adapters. However, for optimum performance, connect HP Surestore DAT
40 devices to an LVD SCSI bus.
We also recommend that the tape drive or autoloader is connected to a
dedicated host bus adapter. If you need to connect multiple devices to the bus,
performance will not be restricted as long as devices are of the same type (for
example, Ultra Wide SCSI). If one device is single-ended, all devices will be
treated as single-ended, which will restrict the maximum permissible length of
the cable and could restrict the performance of HP Surestore DAT 40 devices. It
could take longer to back up your data.
Make sure that the last device on the SCSI bus is terminated. 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 Surestore DAT tape
drives.
what is SCSI?
The Small Computer Systems Interface (SCSI) is popular because it offers a
fast and flexible method of connecting a variety of devices to a host computer.
The SCSI standards define both the physical connections between the devices
(cables and connectors) and the protocols devices use to communicate with
each other.
the standards
There have been three general standards:
SCSI-1, which is now obsolete
SCSI-2, which is very common, and still a current standard
SCSI-3, which is an emerging set of linked standards that define
much more than the simple bus systems used by the earlier versions.
SCSI-3 includes Fibre Channel, Wide SCSI, FireWire (IEE 1398),
Low Voltage Differential (LVD or LVDS), and Fast Serial SCSI. Some
of these standards are now being used on PC platforms
Another variant is ATAPI, which uses an EIDE physical bus to pass SCSI
protocols to connected devices. Technically, this is not part of the SCSI-3
standards, although some operating systems (notably Windows NT) manage
ATAPI devices as if they were fully SCSI.
SCSI is a backward-compatible standard, so that SCSI-2 and SCSI-3 devices
can almost always be made to work together.
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 Adaptec 3940W) 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.
The voltage level of the interface, which may be single-ended (SE) or
low voltage differential (LVD).
As described above, HP Surestore DAT 40 drives and DAT 40x6 autoloaders
are Ultra Wide SCSI devices designed to operate on a low voltage differential
SCSI interface. HP Surestore DAT 24 drives and DAT 24x6 autoloaders are
Fast SCSI devices designed to operate on a Fast SCSI interface.
setting up the SCSI bus
Each device on a SCSI bus, including the SCSI host bus adapter (HBA), must be
configured with a unique ID (identifier). The SCSI bus must be terminated.
Note: HP recommends that a dedicated host bus adapter is used for the tape
drive. A suitable adapter is available from HP as an accessory (see
Ordering
Information).
SCSI ID numbers
For wide SCSI buses, the SCSI ID will be a number from 0 through 15, so a
typical wide SCSI HBA can accommodate up to fifteen other devices.
SCSI IDs are usually set on the device itself (sometimes via configuration
software), but some newer devices are capable of selecting an unused ID
automatically when powered-up (these are known as "SCAM" devices). HP
Surestore drives are SCAM-1 compliant. This means that the drive will return its
SCSI ID to the host bus adapter in response to a SCSI inquiry, but it will not allow
the adapter to change the SCSI ID.
SCSI ID 7 is normally reserved for the HBA because it has the highest priority on
the bus. On wide buses, the priority runs from 7 (highest) to 0, then 15 down to 8
(lowest).
Note: As a general rule, avoid putting tape devices on the same bus as any hard
disks.
identifying SCSI IDs
If your computer already has devices connected to the SCSI bus, you will need to
know their IDs to avoid any conflict with the new tape drive. Here are some
methods of finding out the information:
The fastest and easiest way is to run HP Library & Tape Tools from
this CD-ROM. HP Library & Tape Tools will check your SCSI
configuration, including the SCSI controller itself and any devices
currently attached to it.
Most computers display a list of SCSI devices and IDs during the
boot-up process. This usually scrolls past very fast. If you press the
[Pause] key, you should be able to halt the scrolling and view the list.
If you have an Adaptec host adapter in the computer, it may have
come with a Windows utility called SCSI Interrogator
(SHOWSCSI.EXE) which displays information about connected
devices.
If you have Windows NT installed, select SCSI Adapters from the
Control Panel, select a device in the Devices tab and click on
Properties to view information about the device, including its SCSI
ID.
If you have Novell NetWare installed, use its LIST DEVICES
command.
If none of these is available to you, try the following sources of information:
The details of all installed devices and settings may have been
written down and stored with your computer's documentation (for
new computers, this is often done by the supplier).
Your HBA's documentation should tell you which settings it uses.
Look at each device to find out its ID. This is usually easy with
external devices. With internal devices, you will probably need the
help of the device's documentation to identify the SCSI ID setting,
which is usually set with jumpers.
setting the scsi id on hp surestore dat drives
For all cases, see the Getting Started Guide that came with your tape drive for
more details. Note that host adapters check SCSI IDs only at power-on, so any
changes will not take effect until the host system is power-cycled.
On internal HP Surestore drives, set the SCSI ID by attaching or
removing jumpers at the rear of the drive.
On external HP Surestore drives, the ID is displayed on the rear
panel and can be set by pressing the little buttons above and below
the number.
On removable HP Surestore drives, the ID is set on the back of the
tape array.
SCSI termination
Terminators are essential, as they provide the correct voltages on the SCSI bus
and prevent unwanted signal reflections from interfering with data transfers. The
rule is:
There must be termination at both physical ends of the bus
and only at the ends.
There are two main types of termination, active and passive. Active terminators
reduce interference and allow faster data throughput. On devices with high
transfer speeds, such as HP Surestore DAT 40 and DAT 24 devices, active
termination is required. Multi-mode active terminators are used with ultra wide
LVD SCSI buses. These terminators detect the type of bus and automatically
supply the correct termination
Normally the HBA forms one end of the SCSI bus and provides termination.
You, therefore, need to ensure that the other end of the bus is terminated.
internal drives
Usually the internal SCSI cable in a
server has a number of SCSI
connectors along its length and a
terminator at the end farthest from the
host bus adapter. This will usually be a
small, rectangular block of plastic
attached to the cable end and marked
‘SCSI Terminator’.
As long as this terminator is attached,
you do not need to take any further
action. However, if you have other
devices attached to the cable, make
sure that they have termination
removed or disabled.
Note: If you have an internal and external device attached to the same SCSI
bus, the HBA will be in the middle of the cable and thus its termination must be
disabled. See the host bus adapter's documentation for details of how to do
this.
external drives
All HP Surestore DAT external tape drives and autoloaders are supplied with
the appropriate terminators.
Make sure the terminator is firmly attached to the SCSI-OUT connector on the
rear of the device when you install it. With the HP Surestore DAT 40 and DAT
40x6 always use the supplied multi-mode terminator for proper operation.
If you have more than one device on the SCSI bus, daisy-chain them by
connecting a cable from the SCSI-OUT connector on the first device to the SCSI-
IN connector on the second device and make sure that the second device is
terminated. (For HP Surestore DAT 40 devices, use an LVD-rated cable and an
LVD-rated multimode terminator.)
removable drives
For HP Surestore 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 Surestore DAT internal devices, you need a SCSI ribbon cable with the
correct termination. HP Surestore DAT 40 and DAT 40x6 drives have a 68-pin
wide, high-density SCSI connector. If you are using an HP Surestore DAT drive
on an internal bus with other peripherals that run at Ultra or Ultra2 speeds, it is
important that a 68-pin LVD-compatible ribbon cable is used. If your computer
uses narrow SCSI, you will need a cable or adapter that enables you to connect a
wide SCSI device (68 pins) into the narrow SCSI bus (50 pins). This can be
purchased from your supplier.
HP Surestore DAT 24 and DAT 24x6 devices have a 50-pin narrow SCSI
connector. If your computer uses wide SCSI, you will need a cable or adapter that
enables you to connect a narrow SCSI device (50 pins) into the wide SCSI bus
(68 pins). This is provided with your tape drive.
with external devices
The cable provided with all HP Surestore DAT external tape drives and
autoloaders will attach to a computer with a wide LVDS SCSI connector (68 pins).
with VHD connector
If your server or host bus adapter is equipped with a very high density (VHD) wide
SCSI connector, you will need to order a 68-pin HD-to-VHD converter or 68-pin
HD-to-VHD cable. See
Ordering Information.
with removable devices
For HP Surestore DAT removable tape drives, appropriate cables 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 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 Ultra2 speeds will be enabled. You can use a combination of
Ultra and Ultra2 devices. Each device will operate at its optimum speed.
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