Zaxxon,
you can have other volume managers on AIX too - I have plenty of systems running Veritas Volume Manager and Veritas filesystems - and other servers out of any volume manager using ASM ...
Michal,
first of all you should determine if all filesystems you want to extend are in rootvg
# lsvg -l rootvg # shows you your filesystem
# lsvg rootvg # shows you how much space is used/free/available at all
# chfs -a size=+xG # extends your filesystem by x GB
# chfs -a size=-xG # reduces your filesystem by x GB (given using jfs2)
# extendvg rootvg hdiskx # adds a further disk to your vg in case you do not have free space - but since your filesystems appear all to be very tiny, I would not assume that you should have issues extending it anyway
no need for any reboot while working with lvm - and no need to copy anything anywhere ...
you can make more space in /usr by either committing applied packages or just doing nothing - you usually only need more space there while installing new software and with the -X flag during install the filesystem will be automatically extended anyway
you might want to have a look into this redbook since you seem to be very new on AIX anyway ?
http://www.redbooks.ibm.com/redbooks/pdfs/sg245433.pdf
kahoona,
why is it bad style to have mountpoints under existing mountpoints IN ROOTVG - especially when you have your homedirs in automounts its probably the best idea you can have - and when you're creating your submounts the properway /letting ODM know about - not manipulating /etc/filesystems manually - that will never be a problem when you have setup your system thoughtfully?
Kind regards
zxmaus