If you are working with a volume group that uses RAID5 or RAID6, that is probably correct. It can take a very long time and you cannot interrupt it once it is started. If increasing LUN (volume) size is something you will need to do on a regular basis, I would suggest reconfiguring your array to use DDP. Then increasing the size of a LUN is very fast. This is one of the reasons DDP was created, to allow for dynamic (easy) expansion of the pool size and the volume sizes among other things.