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IBM-AUSTRIA - PC-HW-Support 30 Aug 1999 |
SCSI Drives
SCSI Drives
Some drives have a special design called
small computer system interface , or 'SCSI.' This
design allows you to attach multiple drives to a single
SCSI-2 adapter.
NOTE:
Any information about SCSI drives also applies to other
SCSI devices, such as scanners and printers.
The server comes with a SCSI-2 adapter. The number of
preinstalled SCSI hard disk drives varies according to model.
If you install additional SCSI devices, each SCSI device that is
connected to the adapter needs a unique identification (ID) so that
the SCSI-2 adapter can identify the devices and ensure that
different devices do not attempt to transfer data at the same time.
If you need to set IDs for SCSI devices, refer to the instructions that
came with those devices.
The server automatically sets SCSI IDs for hot-swap drives.
These IDs are determined by the drive locations in the bays.
The SCSI ID for the preinstalled 4X CD-ROM drive in bay A is set to
6, and the SCSI ID for the SCSI-2 adapter is set to 7.
The processing sequence for SCSI devices is set
according to their IDs.
Through the SCSISelect utility program, you can specify
the scanning order for these devices. That is, you
can specify whether the scanning sequence proceeds from 0 to the
highest-numbered SCSI ID, or whether it proceeds in descending order.
The standard scanning sequence proceeds from 0 to 6, then 8 to 15.
However, this convention does not apply if you use the
reverse scan feature of the SCSISelect Utility program.
Use the processing sequence that best suits the system configuration.
See 'Configure/View Host Adapter Settings' for information about setting the scanning
order.
The SCSI-2 adapter has both internal and external ports.
Depending on the server configuration,
you can attach additional SCSI drives
by chaining them (connecting them together with cables).
Depending on the type of SCSI-2 adapter installed in the server,
the adapter supports a total of 14 or 15
SCSI drives (internal and external).
To configure the SCSI devices that you install in a
non-disk-array model, use the built-in SCSI-2 adapter utility
program, SCSISelect. See 'SCSISelect Utility Program' .
For disk-array models use the RAID configuration program. See 'Disk Array Configuration'
There are two types of SCSI devices: wide and narrow.
You must use 16-bit cables to attach wide devices.
Use 8-bit cables to attach narrow devices.
Wide device IDs can be set to any number from 0 to 15. Narrow
devices can only have their IDs set from 0 to 7.
The preinstalled 4X CD-ROM drive in bay A is a narrow device.
Two devices connected to the same bus (internal or external) cannot
have the same ID, however, you can use the
same ID for an internal device and an external device. The
primary partitions on SCSI drives that are connected to the internal
bus on a given adapter are assigned drive letters before the external
drives that are connected to the same adapter are assigned drive
letters. If multiple adapters are installed in the server, the drives
that are connected to the adapter in the lowest number
expansion slot are assigned drive letters first.
When SCSI devices are chained, both
ends of the chain (cable) require a terminator .
The purpose of these terminators is to ensure that the quality
of the signal is maintained throughout the SCSI chain.
If you attach SCSI devices (internal or external),
you must terminate the last device in the chain,
or the end of the cable must be terminated.
NOTE:
The backplanes automatically set termination for all the drives in the
hot-swap bays.
The SCSI-2 adapter automatically adjusts for termination.
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