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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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