hard disk -- Technical Information

The hard disk is the primary  means of storing and accessing data under the
COHERENT  system.  This  article introduces  some  aspects of  the COHERENT
system that affect the care and feeding of your hard disk.

Device Drivers

The COHERENT system comes with two  drivers for hard disks: the at drivers,
for AT-style hard disks (i.e., IDE,  ESDI, MFM, or RLL disks); and hai, for
the  SCSI family  of hard  disks.  hai is  a host  adapter-independent SCSI
driver and  also supports  SCSI devices other  than hard disks,  e.g., SCSI
tape.  which is the old-style driver for Adaptec SCSI devices.  For details
on each driver, see its entry in the Lexicon.

The following  describes how to enable or disable  a given hard-disk driver
in  your  kernel.   To disable  a  hard-drive  controller,  log  in as  the
superuser root and then execute the following commands:

    cd /etc/conf
    bin/idenable -d disk_driver
    bin/idmkcoh -o /kernel_name

where  kernel_name is  the name  you wish  to give to  the new  kernel, and
disk_driver is one of at, aha, ss, or hai.

To  enable a  hard disk,  again  log in  as root;  then type  the following
commands:

    cd /etc/conf
    bin/idenable -e disk_driver
    # if you are installing the hai driver:
    # hai/mkdev
    bin/idmkcoh -o /kernel_name

where disk_driver is one of at, aha, ss, or hai.

Partitioning

The COHERENT command fdisk displays information about how your hard disk is
currently configured.   You can also  use it to repartition  your hard disk
and reassign partitions from MS-DOS to COHERENT, or vice versa.

This  is an  extremely powerful  command,  with which  you can  create much
mayhem  on your  system.   Like any  powerful  tool, it  should be  treated
carefully and  with respect.  See the  article on fdisk in  the Lexicon for
details on how to use this command.

Partitioning your  hard drive can be an  uncomplicated procedure.  We offer
these guidelines  in an effort  to make it  as simple as  possible.  Before
attempting any partitioning you should first back-up all the data currently
on  your  hard  drive.   If  you  do  not do  this  you  risk  losing  data
permanently.  You should also  know the correct physical parameters of your
hard  drive.    This  information  can   be  obtained  from   your  machine
documentation or  from the drive manufacturer.   It is best not  to rely on
the parameters given in the BIOS: these may be translation parameters.

If your drive is formatted for  MS-DOS, it is advisable to run MS-DOS fdisk
before you  start to install COHERENT.   If the whole drive  is taken up by
DOS partitions, you  must use MS-DOS fdisk to create  a non-DOS area on the
drive.  It  is not  sufficient to  have an empty  MS-DOS logical  drive set
aside for COHERENT.  COHERENT  does not recognize MS-DOS logical drives, it
only sees the whole partition.  The following diagram shows the way the MS-
DOS fdisk sees your drive:



        ===========================
        |    DOS Root Partition   |
        |=========================|
        |  DOS Extended Partition |
        |=========================|
        |  =====================  |
        |  |  Logical Drive 1  |  |
        |  =====================  |
        | - - - - - - - - - - - - |
        |  =====================  |
        |  |  Logical Drive 2  |  |
        |  =====================  |
        | - - - - - - - - - - - - |
        |  =====================  |
        |  |  Logical Drive 3  |  |
        |  =====================  |
        ===========================

And the following diagram shows the way the COHERENT fdisk sees your drive:



        ===========================
        |    DOS Root Partition   |
        |=========================|
        |                         |
        |                         |
        | DOS Extended Partition  |
        |                         |
        |                         |
        ===========================

If you use COHERENT fdisk to repartition MS-DOS space, you risk causing MS-
DOS fdisk to hang.  One further  word of warning.  If you have an automated
disk formatting  and partitioning utility on your  MS-DOS partition such as
Disk Manager or Speedstor, you should operate it in ``manual'' mode, not in
``automatic''.

Some  hard  drives  have more  than  1,024  cylinders.   COHERENT can  only
recognize  a drive  up  to this  limit.   You may  have a  utility such  as
Speedstor that allows you  to place MS-DOS partitions beyond that boundary.
COHERENT will  not see those partitions,  but you can still  access them as
usual through MS-DOS.

When partitioning  a drive with more  than 1,024 cylinders, be  sure to run
the partitioning utility before  you start to install COHERENT.  You should
create a non-DOS  partition that falls completely within the 1,022-cylinder
boundary.   Your next  MS-DOS  partition should  start no  sooner than  the
1,026th cylinder.

Adding a COHERENT Partition

The following  describes how to add  a new COHERENT partition  on your hard
disk.

During  your initial  installation  of COHERENT,  the installation  program
handled the  details of  preparing your hard  disk for COHERENT.   Adding a
partition after  the system is installed is not  difficult, but it requires
that  you understand  the  operation of  the  following commands:  badscan,
chmod, chown,  fdisk, fsck, mkfs,  and mount. See the  Lexicon articles for
each of these commands for further  information before you attempt to add a
partition.

In general, the following steps  are required when creating a partition for
use by  COHERENT.  Please note  that you must  not change the  size of your
existing root partition, or you may no longer be able to boot COHERENT from
the hard disk.

1. Completely back up all partitions on your hard disk.  Be sure to back up
   the COHERENT  partitions, as well as  any non-COHERENT partitions (e.g.,
   those for  MS-DOS or OS/2).   Verify that your backups  are readable and
   correct.

2. Log in  as the  superuser root.  Make sure all  other users are  off the
   system; then invoke  the command /etc/shutdown. This shuts down COHERENT
   and returns  the system to  single-user mode.  Type the  command sync to
   flush all buffers.

3. Invoke the COHERENT command fdisk and add the COHERENT partition to your
   disk,  as  described above.   Be  sure  to write  down  the device  name
   associated with your new partition (e.g., /dev/at0c) and its size.

4. The command badscan checks the device for bad blocks.  If your partition
   resides on a non-SCSI device, run the command badscan as follows:

       /etc/badscan -v -o /conf/proto.device raw_device xdevice

   where device specifies  the four-character block-special device name for
   the partition (e.g., at0c), raw_device  is the full device path name for
   the  character-special  device  associated  with  the  partition  (e.g.,
   /dev/rat0c), and  xdevice names the partition-table  device for the disk
   drive (e.g., /dev/at0x).

5. Invoke the  command mkfs  to create  a COHERENT file  system on  the new
   partition, as follows:

       /etc/mkfs /dev/device /conf/proto.device

   This invocation  forces mkfs to  use the contents of  the ``proto'' file
   that  badscan created  when  it built  the  bad_block list  for the  new
   partition.

6. If need  be, use  the command mkdir  to create a  directory to use  as a
   mount point for  the newly created file system.  The  mount point is the
   directory  onto which  this directory's  file  system will  be appended.
   Usually,  this directory  is  located under  `/', also  called the  root
   directory.  You  can, however,  mount a  file system onto  any directory
   that  already  exists.  If  you  create  a new  directory  (e.g., /w  or
   /mydir),  use  the  commands  chown  and  chmod to  set  an  appropriate
   ownership and mode for for the directory.

7. Edit the file /etc/mount.all and add a line of the following form:

       /etc/mount device /mount_point

   where device is the full path name of the device that specifies your new
   partition  (e.g.,  /dev/at0c),  and  mount_point  is  the  name  of  the
   directory that you created in the earlier step.

8. Finally,  edit the  file /etc/checklist  and  add the  character special
   device  name (e.g.,  /dev/rat0c) of  the new  COHERENT partition  to it.
   This  will ensure  that  COHERENT will  automatically run  fsck on  that
   partition's file system whenever you boot the system.  This can be vital
   in recovering from a system crash.

Adding Another Hard Disk

If you  wish to add another  hard disk to your system, you  may have to run
some low-level routines  that are hardware specific.  See the documentation
that accompanies your hardware for details.

In brief, when you install the hard disk, you must partition it, as you did
your original hard disk when you  first installed COHERENT.  If you wish to
add non-COHERENT operating systems to  one or more partitions, do so first;
then add COHERENT to the remaining partitions, as described above.

Changing the Size of the Root Partition

Changing  the size  of your  root file system  requires that  you reinstall
COHERENT.  It is  strongly advised that you back up  all partitions of your
system before  you attempt  to do  this.  In addition,  to reduce  the time
involved in  restoring your  data files, make  an additional backup  of all
directories  and  files  that  have  changed  form your  original  COHERENT
installation.  The  command find will  help you locate all  such files; see
its Lexicon entry for details.

You  should then  follow  the directions  given  in the  release notes  for
installing COHERENT.   Note that when you attempt  to install COHERENT over
an existing COHERENT  partition, COHERENT will ask you if  you are sure you
know what you're doing before the installation procedure creates a new file
system on  the partition.   Be sure  to request that  a new file  system be
created, or the installation will fail.

After installing  the COHERENT distribution  onto your new  root partition,
restore any data files and directories  from the second set of backups that
you performed.

See Also

Administering COHERENT,
at,
badscan,
chmod,
chown,
fdisk,
fsck,
hai,
ideinfo,
mkfs,
mount

Notes

For information on how an IDE drive is configured, use the command ideinfo.
For details on how to use this command, see its entry in the Lexicon.

Some  users have  attempted to  use  Norton Utilities  or similar  tools to
rearrange the partition table, only  to find that COHERENT no longer boots.
That is because the kernel has embedded within it the name of the partition
on which  it and its root  file system live.  By  using Norton Utilities to
shuffle the partition table, the kernel  will no longer be able to find any
of the files or utilities it  needs to boot your system.  If you still wish
to shuffle your  disk's partition table, be sure to  change the name of the
root device within the kernel before you change the partition table.

© 2012 by Stephen A. Ness