Below is the command used to create a volume group from one or more physical volumes.

vgcreate vg1 /dev/device1 /dev/device2

When physical volumes are used to create volume group, the disk space is divided into 4mb extents. This means that the logical volumes are increased and decreased by this size.

Logical Volume groups will be represented as:

/dev/vg/lv/

For example if you create 2 volume groups and 3 logical volumes it will be displayed as:

/dev/vg1/lv01
/dev/vg1/lv02
/dev/vg1/lv03
/dev/vg2/lv01
/dev/vg2/lv02
/dev/vg2/lv03

Below is how to extend a volume group by adding another physical volume:

vgextend vg1 /dev/device4

There are 2 commands you can use to display the current groups:
The vgs command provides volume group information in a configurable form, displaying one line per volume group

vgs

The vgdisplay command displays volume group properties (such as size, extents, number of physical volumes, etc.) in a fixed form

vgdisplay

If you wish to remove a physical device from a volume group you will first need to make sure that the device is not being used. If the device IS being used then you will need to move the data off (pvmove). Below shows an output of a full device.

pvdisplay /dev/device2

Example output:

-- Physical volume ---
PV Name               /dev/device2
VG Name               vg
PV Size               1.95 GB / NOT usable 4 MB [LVM: 122 KB]
PV#                   1
PV Status             available
Allocatable           yes (but full)
Cur LV                1
PE Size (KByte)       4096
Total PE              499
Free PE               0
Allocated PE          499
PV UUID               Sd44tK-9IRw-SrMC-MOkn-76iP-iftz-OVSen7

Once you move off the data you can use vgreduce:

vgreduce vg1 /dev/device2