IBM 847661U Hardware Maintenance Manual - Page 112

SCSI drives, SCSI physical unit numbers

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SCSI drives: Some drives have a special design called small computer system interface (SCSI). This design allows you to attach multiple drives to a single connector. Note Any information about SCSI drives also applies to other SCSI devices, such as scanners and printers. The Netfinity 3000 server supports drives that comply with American National Standards Institute (ANSI) SCSI Standards X3.131-1986 (SCSI), X3.131-1994, (SCSI-2), X3.277-1996 (SCSI-3 Fast-20 parallel interface), and X3.253-1995 (SCSI-3 parallel interface). For a complete list of the SCSI devices that the server supports, go to http://www.ibm.com/pc/us/netfinity/ on the World Wide Web. SCSI physical unit numbers: When more than one physical device is connected to the same UltraSCSI adapter, the devices compete for support from the UltraSCSI adapter. Because the UltraSCSI adapter communicates with only one device at a time, the priority of a device is based on its SCSI identification (ID). The highest priority IDs are 7 to 0; the lowest priority IDs are 15 to 8. If you install additional SCSI devices, you must set a unique ID for each SCSI device that you connect to the integrated SCSI-2 connector. This unique ID enables the UltraSCSI adapter to identify the devices and to prevent two devices from sending or receiving data on the SCSI bus at the same time. SCSI devices use a variety of methods to set the SCSI ID, such as jumpers, thumbwheels, or switches. The SCSI device ID is also known as the SCSI address or physical unit number (PUN). The UltraSCSI adapter in the server supports SCSI IDs 0 to 15; ID 7 is reserved for the adapter. The default startup (boot) SCSI ID is 0 for an internal SCSI hard disk drive in Channel A. Use SCSISelect to view the SCSI IDs of SCSI devices in the server. (See "SCSISelect utility program" on page 49 for more information.) If you install wide (16-bit) SCSI devices, you can set the IDs to any number between 0 and 6, or between 8 and 15. If you install narrow (8-bit) SCSI devices, you can set the IDs to any number between 0 and 6. SCSI logical unit number: Each physical device has a physical unit number (PUN) and a logical unit number (LUN). If a physical device supports no logical devices, its LUN is 0. Most SCSI devices support only LUN 0. 104 Netfinity Server HMM

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SCSI drives:
Some drives have a special design
called
small computer system interface
(SCSI). This
design allows you to attach multiple drives to a single
connector.
Note
Any information about SCSI drives also applies to
other SCSI devices, such as scanners and printers.
The Netfinity 3000 server supports drives that comply with
American National Standards Institute (ANSI) SCSI
Standards X3.131-1986 (SCSI), X3.131-1994, (SCSI-2),
X3.277-1996 (SCSI-3 Fast-20 parallel interface), and
X3.253-1995 (SCSI-3 parallel interface).
For a complete list of the SCSI devices that the server
World Wide Web.
SCSI physical unit numbers:
When more than one
physical device is connected to the same UltraSCSI
adapter
, the devices compete for support from the
UltraSCSI adapter.
Because the UltraSCSI adapter
communicates with only one device at a time, the priority
of a device is based on its SCSI identification (ID).
The
highest priority IDs are 7 to 0; the lowest priority IDs are
15 to
8.
If you install additional SCSI devices, you must set a
unique ID for each SCSI device that you connect to the
integrated SCSI-2 connector.
This unique ID enables the
UltraSCSI adapter to identify the devices and to prevent
two devices from sending or receiving data on the SCSI
bus at the same time.
SCSI devices use a variety of
methods to set the SCSI ID, such as jumpers,
thumbwheels, or
switches.
The SCSI device ID is also known as the SCSI
address
or
physical unit number
(PUN).
The UltraSCSI adapter in the server supports SCSI IDs 0
to 15; ID 7 is reserved for the adapter.
The default startup
(boot) SCSI ID is 0 for an internal SCSI hard disk drive in
Channel A.
Use SCSISelect to view the SCSI IDs of SCSI
devices in the server.
(See “SCSISelect utility program” on
page
49 for more information.)
If you install wide (16-bit) SCSI devices, you can set the
IDs to any number between 0 and 6, or between 8 and 15.
If you install narrow (8-bit) SCSI devices, you can set the
IDs to any number between 0 and 6.
SCSI logical unit number:
Each physical device has
a physical unit number (PUN) and a logical unit number
(LUN).
If a physical device supports no logical devices, its
LUN is 0.
Most SCSI devices support only LUN 0.
104
Netfinity Server HMM