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