Throughout the life of a volume group (VG) can happen a lot. The most common are in relation to its size or its physical volumes. Ah, I can hear a lot of you thinking about how to expand their volume :).
When changing the size of a physical volume (PV) AIX does not realize it hot. In AIX boxes it is common that the disk is coming from an external storage (Ex: SAN) and some of the LUNs which correspond to devices that exist in hdiskX VG has been expanded. We recalculate the size of available disk with the following:
# Chvg -g
For more info about Chvg check out: IBM Pseries Chvg.