Ref: 13420005
Title: "Error Loading Boot Sector" Message on 3S/401 Servers
date: 11/07/89

Copyright 3Com Corporation, 1991.  All rights reserved.

After exchanging hard disk drives in the base unit of a 3S/401 server, the
message "error loading boot sector" appears on the server's LCD during the
server boot process.  This happens when dissimilar drives are exchanged (for
example, when a 150 MB drive is swapped for a 320 MB or 630 MB drive).

The problem occurs because the drives have different numbers of cylinders and
heads.  If the drive is configured improperly, it is unbootable.  To solve the
problem, 3DISK386 must be run and the drive must be removed from the drive
table, then added in again to update the CMOS on the server.  The following
steps show how to redefine the boot drive:

1.  Establish a console connection and run 3DISK386 from the System Software
#1 disk (P/N 3382-07 for 150 MB and 320 MB drives or P/N 3382-08 for 630 MB,
320 MB, and 150 MB drives).

2.  Select option 2 (Configuration).

3.  From the Configuration menu, select option A (Display Configuration).

4.  Write down all the SCSI and LUN numbers for your server including
those for the expansion unit if you have one.

5.  Select option F (Remove All Drives).

(See the end of this article for a detailed explanation of why this must be
done.)

6.  Respond with a Y(es) to the "Continue?" prompt.

7.  Select option B (Add Drive).

8.  Enter 2 for SCSI ID.

9.  Enter 0 for LUN.

10. Select Adaptec ACB-4525 for controller type.

11. Add all remaining drives if you have an expansion unit.

12. Select option D (Choose Boot Disk).

13. Select the appropriate drive and controller combination that you have in
the base unit.

14.  Press ESC twice to get out of 3DISK386.

15.  Reset your server.

Now the server should know the kind of drive it has and where the boot
sector resides.


Replacing Hard Drives

When replacing hard drives, make sure that the controller that
came with the drive is used.  The ROM on the Adaptec 4525
controller has several revisions.  If you have a controller with
a rev B ROM, it will only support a 150 MB drive.  To support a
320 MB drive, you need a rev C ROM and for the 630 MB drive, a rev
D is required.  The ROMs are all downwardly compatible so the rev
D ROM can support either the 630 MB, 320 MB or 150 MB drive.

When an existing drive is replaced with a larger drive, there may not
enough memory to support it.  The CIOSYS buffers allocated for the smaller
drive may not be enough for the larger partitions.  We recommend that
the larger drives (for example, 320 MB and 630 MB) be formatted so they
have larger partitions than normal.  (Note, however, that the C: partition
should always stay at 32 MB or less.)  The reason for larger partitions is
that our servers will support only 24 DOS drive identifiers (C:-Z:) and, if
you have more than one drive on a server, you will run out of identifiers for
all the partitions.  Larger partitions will require different bytes-per-sector
and sector-per-cluster sizes.  Because of this, the buffer pools will be
different and many more buffers are needed when CIOSYS sets up the buffer
pools.  We recommend that the amount of memory in the server be increased
when you install larger drives in the base unit or the expansion unit.


Removing All Drives

All drives must be removed because the drive list is kept in sequential order
in CMOS.  For example, if we had two drives on a server, they would have two
different SCSI ID numbers as shown in the following sample CMOS list:

        SCSI ID /LUN       Controller Type
        ------------       ---------------
            2/0             Adaptec 4525
            3/0             Adaptec 4525

The first entry is always the boot device and in this case, it would be the
base unit's drive.  If we used option C (Remove a Drive) instead of F (Remove
all Drives and clear CMOS) to remove 2/0, only 2/0 would be removed.  Then,
the expansion unit's drive 3/0 would automatically move up into the first
position and the server would try to use that drive as its boot device,
which would not work.  If we then re-added drive 2/0, the CMOS list would
have this entry:

        SCSI ID /LUN        Controller Type
        ------------        ---------------
            3/0              Adaptec 4525
            2/0              Adaptec 4525

As you can see, by adding 2/0 back in, the entry is put at the end of the
list and the server still attempts to use 3/0 as its boot device.  To make
sure that 2/0 is at the top of the list, remove ALL drives, then add them
back in order.

