NOTE:  This document was written for VxVM 2.x.  New functionality in
       VxVM 3.x renders many of the "extra steps" in replacing a
       primary root disk obsolete.  See the comments interspersed
       below regarding steps when using VxVM 3.x.

If Volume Manager (VxVM) is running on a system with the root disk
encapsulated and mirrored, and the root disk fails, the system stays 
up and running, due to the fact that it is mirrored, but how can you 
recover the original root disk?

First, some terminology:

   The 'primary' root disk is the system disk on which the OS was
   originally installed.  This disk was "encapsulated" into VxVM and
   then mirrored.  Since this disk is encapsulated, there is a
   direct mapping of partitions onto volumes for /, swap, /usr, and
   /var.

   The 'secondary' root disk is a disk which was first initialized into
   VxVM and then used to form a mirror for the primary root disk.

   VxVM 2.x: Since it was initialized, rather than encapsulated, there
   is no mapping of partitions onto the volumes /, swap, /usr, and /var.
   VxVM 3.x: When the mirror of the root disk is created, the mapping
   of partitions onto the volumes /, swap, /usr, and /var is maintained.


RECOVERING THE 'SECONDARY' BOOT DISK:

   If the 'secondary' system disk fails, the replacement of the disk is
   straightforward.  It is handled in the same manner that any other
   failed drive needs to be replaced.

   The easiest way to do this is to run 'vxdiskadm' and choose option
   #4 (Remove a disk for replacement).  Then, shut down the system (if
   necessary) to physically replace the disk, and reboot.

   Run 'vxdiskadm' again, this time choosing option #5 (Replace a
   failed or removed disk).  When asked to 'encapsulate' the disk,
   reply "no", and then reply "yes" when asked if you wish to
   initialize it.

   This will begin recovery of the disk and the mirrors will resync
   automatically.


RECOVERING THE 'PRIMARY' BOOT DISK:

   NOTE: If you are running Volume Manager version 3.x.x or above, it
   is not necessary to follow the steps below.  Instead, the process
   for replacing the 'primary' boot disk is EXACTLY the same as that
   for the 'secondary' boot disk, which is shown above.  The reason
   for this is because Volume Manager 3.x automatically creates the
   underlying "hard" partitions for /usr and /var on the replacement
   disk, whereas older versions did not.

   If you are using Volume Manager 2.x, continue on:

   The recovery of the 'primary' boot disk contains a few additional
   steps because the procedure must reestablish the direct mapping
   between the partitions on the disk and the system volumes.  This is
   necessary so that the system can be changed back to use underlying
   devices, should this be necessary (for example, to perform a system
   upgrade or boot from cdrom to fsck one of these filesystems).

   1.  Run 'vxdiskadm' and choose option #4 (Remove a disk for
       replacement).  Then, shut down the system (if necessary) to
       physically replace the disk, and reboot.

   2.  Run 'vxdiskadm' and choose option #5 (Replace a
       failed or removed disk).  When asked to 'encapsulate' the disk,
       reply "no", and then reply "yes" when asked if you wish to
       initialize it.

   3.  This step will change depending on the number of partitions on
       the boot disk.  The 'vxdiskadm' command will put back partition
       0 (for /) automatically, and may also do this for swap.
       However, if you have any additional volumes on that disk (i.e.,
       /usr or /var), you will have to run a command to put the
       partition on the new disk in the correct location.

       Examine the partitions on the replaced disk by running 'format'
       or 'prtvtoc' on it.  At the very least, you will see a partition
       for root and one for the public and one for the private
       partitions for VxVM.  Determine if any partitions are missing.
       If so, these "missing" partitions can be recreated easily using
       the steps below.

       The command to use is 'vxmksdpart'.  You give this
       command the name of a particular subdisk, and it creates a
       partition on the disk in the correct location.  The syntax is:

          /etc/vx/bin/vxmksdpart <subdisk> <partition> <tag> <flags>

       For example, if you have a subdisk named "disk01-02" and wanted
       to create partition 7 on the disk to map this subdisk, you can run

          /etc/vx/bin/vxmksdpart disk01-02 7 0x00 0x00

   3a. SWAP.  To create a partition for the swap volume, run:

          /etc/vx/bin/vxmksdpart -g rootdg <subdisk> <partition> 0x03 0x01

       where <subdisk> is the name of the subdisk used in the swapvol
       volume on the primary boot disk (for example, "rootdisk-01"),
       and <partition> is the unused partition to use for swap (for
       example, "1").  The "0x03" tag specifies this partition is for
       'swap'.

   3b. USR.  To create a partiton for /usr (if this disk contains /usr), run:

          /etc/vx/bin/vxmksdpart -g rootdg <subdisk> <partition> 0x04 0x00

   3c. VAR.  To create a partiton for /var (if this disk contains /var), run:

          /etc/vx/bin/vxmksdpart -g rootdg <subdisk> <partition> 0x07 0x00


       There is no reason to create any other partitions on the boot disk.