HPUX : USAGE of vgchgid (man vgchgid)

DESCRIPTION

      The vgchgid command is designed to change the LVM Volume Group ID

      (VGID) on a supplied set of disks.  vgchgid will work with any type of

      storage, but it is primarily targeted at disk arrays that are able to

      create "snapshots" or "clones" of mirrored LUNs.  vgchgid accepts a

      set of raw physical devices and ensures that they all belong to the

      same volume group, before altering the VGID (see WARNINGS section).

 

      The same VGID is set on all the disks and it should be noted that in

      cases of multi-PV volume groups, all the physical volumes should be

      supplied in a single invocation of the vgchgid command.

 

    Background

      Some storage subsystems have a feature which allows a user to split

      off a set of mirror copies of physical storage (termed BCVs, BCs, or

      Snapshots) just as LVM splits off logical volumes with the lvsplit

      command.  As the result of the "split," the split-off devices will

      have the same VGID as the original disks.  vgchgid is needed to modify

      the VGID on the BCV devices.  Once the VGID has been altered, the BCV

      disks can be imported into a new volume group by using vgimport.

 

      Once the VGID has been changed, the original VGID is lost until a disk

      device is re-mirrored with the original devices.  If vgchgid is used

      on a subset of disk devices (for example, two out of four disk

      devices), the two groups of disk devices would not be able to be

      imported into the same volume group since they have different VGIDs on

      them.  The solution is to re-mirror all four of the disk devices and

      re-run vgchgid on all four BCV devices at the same time, and then use

      vgimport to import them into the same new volume group.

 

      If a disk is newly added to an existing volume group and no subsequent

      LVM operations has been performed to alter the structures (in other

      words, operations which perform an automated vgcfgbackup(1M)); then it

      is possible a subsequent vgchgid will fail.  It will report that the

      disk does not belong to the volume group. This may be overcome by

      performing a structure changing operation on the volume group (for

      example, using lvcreate).

 

EXAMPLES

      An example showing how vgchgid might be used:

 

      1. The system administrator uses the following commands to create the

         Business Continuity (BCV or BC) copy:

 

         1)   For EMC Symmetrix disks, the commands are BCV establish and

              BCV split.

 

         2)   For XP disk array, the commands are paircreate and pairsplit.

 

         Three BCV disks are created.

 

      2. Change the VGID on the BCV disks.

 

         vgchgid /dev/rdsk/c0t0d0 /dev/rdsk/c0t0d1 /dev/rdsk/c0t0d2

 

      3. Make a new volume group using the BCV disks.

 

         mkdir /dev/vgbcv

         mknod /dev/vgbcv/group c 64 0x040000

 

         NOTE: This step can be skipped as the group file will be created

         automatically.  If the group file is manually created it will have

         different major and minor numbers (see lvm(7)).

 

      4. Import the BCV disks into the new volume group.

 

         vgimport /dev/vgbcv /dev/dsk/c0t0d0 /dev/dsk/c0t0d1 /dev/dsk/c0t0d2

 

      5. Activate the new volume group.

 

         vgchange -a y /dev/vgbcv

 

      6. Backup the new volume group's LVM data structure.

 

         vgcfgbackup /dev/vgbcv

 

      7. Mount the associated logical volumes.

 

         mkdir /bcv/lvol1 /bcv/lvol2

         mount /dev/vgbcv/lvol1 /bcv/lvol1

         mount /dev/vgbcv/lvol2 /bcv/lvol2