Installing SCSI Devices

Installing SCSI Devices

Termination

SCSI chains must be terminated, on both ends, with either a passive, active or forced perfect terminator (FPT). For fast or wide SCSI use active termination.

Usually the device e.g. HDD, tape drive or host adapter will have built-in termination which can be switched on or off via a jumper setting.

The terminators require power from at least 1 device, usually the host adapter. A jumper on each device will set this option.

Setting SCSI ID's

This often causes confusion which I hope to dispell.

Most manufacturers have SCSI devices with 3 jumpers for setting the SCSI ID. The most significant bit (MSB) may start on the left or the right and the jumpers may be numbered differently from the table below (i.e. not 0,1,2). The MSB is the highest value bit, in the table below the MSB is on the right & is a 2 (top row, 4th column).

The 0 or 1 denotes jumper on or off.

SCSI ID	0	1	2	Notes
0	0	0	0	All jumpers off
1	1	0	0
2	0	1	0
3	1	1	0
4	0	0	1
5	1	0	1
6	0	1	1
7	1	1	1	Usually reserved for host adapter

Other Jumper Settings

Start Up On Command (Delayed start)

Stops the drive spinnning up when the power comes on, thus reducing the load on the power supply, which can prevent some startup problems. Use when you have several internal HDD's.

SCSI Parity

Basic error checking; set this to on for most modern devices. However, some old host adapters don't support SCSI parity.

SCSI Synchronous Negotiation

Some older devices don't support this.

Tips

Use a permanent marker pen to write the jumper purposes on the drive, so that you can see them when the drive is in the bay. This makes it much easier to change the settings once the drive is installed.

Use a white label on the drive & write in pencil what the SCSI ID etc are.

Use some bent thin nose pliers to remove jumpers.