Installation guide

162 Appendix A:Supplementary Hardware Information
• To disconnect a host bus adapter from a single-initiator bus, you must disconnect the SCSI cable
first from the RAID controller and then from the adapter. This ensures that the RAID controller is
not exposed to any erroneous input.
• Protect connector pins from electrostatic discharge while the SCSI cable is disconnected by wear-
ing a grounded anti-static wrist guard and physically protecting the cable ends from contact with
other objects.
• Do not remove a device that is currently participating in any SCSI bus transactions.
To enable or disable an adapter’s internal termination, use the system BIOS utility. When the system
boots, a message is displayed describing how to start the utility. For example, many utilities will
prompt users to press Ctrl-A. Follow the prompts for setting the termination. At this point, it is also
possible to set the SCSI identification number, as needed, and disable SCSI bus resets. See Section
A.5, SCSI Identification Numbers for more information.
To set storage enclosure and RAID controller termination, see the vendor documentation.
A.4 SCSI Bus Length
A SCSI bus must adhere to length restrictions for the bus type. Buses that do not adhere to these
restrictions will not operate properly. The length of a SCSI bus is calculated from one terminated end
to the other, and must include any cabling that exists inside the system or storage enclosures.
A cluster supports LVD (low voltage differential) buses. The maximum length of a single-initiator
LVD bus is 25 meters. The maximum length of a multi-initiator LVD bus is 12 meters. According
to the SCSI standard, a single-initiator LVD bus is a bus that is connected to only two devices, each
within 0.1 meter from a terminator. All other buses are defined as multi-initiator buses.
Do not connect any single-ended devices to an LVD bus, or the bus will convert to a single-ended bus,
which has a much shorter maximum length than a differential bus.
A.5 SCSI Identification Numbers
Each device on a SCSI bus must have a unique SCSI identification number. Devices include host bus
adapters, RAID controllers, and disks.
The number of devices on a SCSI bus depends on the data path for the bus. A cluster supports wide
SCSI buses, which have a 16-bit data path and support a maximum of 16 devices. Therefore, there are
sixteen possible SCSI identification numbers that can be assigned to the devices on a bus.
In addition, SCSI identification numbers are prioritized. Use the following priority order to assign
SCSI identification numbers:
7-6-5-4-3-2-1-0-15-14-13-12-11-10-9-8