Extending a filesystem on AIX is similar to linux. you add the physical disk to the system. you convert the physical disk to a physical volume (pv) then you add the pv to the volume group (vg) then you extend the logical volume (lv) with the newly assigned space. then you extend the filesystem on the lv.
in the following example we want to add 1Gb to /home/user1. where /home/user1 is an lv by itself. the most common use is normally /oracle in the enterprise (or /u01 or wherever you installed oracle) or /home on the home desktop.
and here are the commands:
1. convert the physical disk to a physical volume
addpv hdisk1
2. add the pv to a volume group
extendvg homevg hdisk100
3. extend the logical volume with the required space. notice that you dont have to commit the whole disk to the lv
extendlv user1lv 10G
4. extend the filesystem on the lv. again you dont have to commit the entire space to the filesystem.
chfs -a size=+1G /home/user1
and there you have it. a disk hdisk1 of unknown size is allocated 10gb to the vg. from there a smaller 1gb is allocated to the users home directory