Ref: 13420017
Title: Selecting Logical Unit Number (LUN) on 3Server Drives
date: 2/22/91

Copyright 3Com Corporation, 1991.  All rights reserved.

A 3Com server can support many hard drives through its use of the SCSI
interface.  It is often desirable to daisy-chain several disk drives together
to get more disk storage on a server.  On a 3S/400-series server, it is
possible to connect only one drive to a controller.  (Limitations on the
3S/400 power supply do not allow it to provide enough power to two disk
drives, the tape drive, and the motherboard at the same time.)  On 3S/500
and 3S/600-series servers, it is possible to connect two drives to one
controller.

When installing the disk drives, it is important to set the Logical Unit
Number (LUN) on the drive.  Selecting the LUN jumper allows one disk
controller to support two drives.  For example, an Adaptec 4525 controller
could have its SCSI address set to 3 and have two drives configured as 0 and
1.  When formatting the drive with 3Disk386, refer to the drives as 3/0 and
3/1.  By allowing two drives on one controller, you can save SCSI addresses,
but there may be a slight bottleneck if the server must access both drives
simultaneously.  The controller will only access one drive at a time.

Note:  The LUN is different from the SCSI address that is selected on the
Adaptec 4525 SCSI-to-ESDI controller card.  Typically the jumper for the LUN
Select (sometimes referred as the Drive Select) is on the back or the bottom
of the disk drive.  Check the following paragraphs to find the jumper
location on each type of drive.

   CDC 150 MB drive:  The jumper block is on the back of the drive above the
20-pin edge connector.  To select LUN=0, place the jumper on the two pins
farthest away from the power connector.  To select LUN=1, move the
jumper to the next adjacent pair of pins.

   Seagate 320 MB drive:  The jumper block is on the back of the drive next
to the power connector.  To select LUN=0, place the jumper on the two pins
closest to the power connector.  To select LUN=1, move the jumper to the next
adjacent pair of pins.

   Seagate 630 MB drive:  The jumper block is on the back of the drive next
to the power connector.  To select LUN=0, place the jumper on the two pins
closest to the power connector.  To select LUN=1, move the jumper to the next
adjacent pair of pins.

   Maxtor 320 MB drive:  The jumper block is labeled DS1, and is located on
the bottom of the drive below the 34-pin edge connector.  To select LUN=0,
place the jumper on the two pins closest to the edge connector.  To select
LUN=1, move the jumper to the next adjacent pair of pins.

   Maxtor 630 MB drive:  The jumper block is labeled DS1, and is located on
the bottom of the drive below the 34-pin edge connector.  To select LUN=0,
place the jumper on the two pins closest to the edge connector.  To select
LUN=1, move the jumper to the next adjacent pair of pins.


Confirming the PROM Version

When replacing or upgrading a drive, it is necessary to have the correct
PROM on the Adaptec controller.

The PROM is located on the controller and is labeled with "Adaptec Inc."
Below the label are eight digits in the form XXXXXX-XX and a letter follows
(B,C,D,E).  The letter indicates what version PROM you have.

If you currently have a 150 MB drive and want to upgrade to a 320 MB drive,
you will need a "C" PROM for the controller.  To upgrade to a 630 MB drive,
you will need an "E" PROM.  (All PROMs are downwardly compatible.)

