Alex Kernel Unix guy

It's good for those working with AIX that it offers Logical Volume Manager. And with help of smitty menus, managing disk space couldn't be ever easier. Since AIX 5.3 you can not only increase the filesystems but there is a possibility to even shrink them. In AIX 5.2 it was needed to do a complete filesystem backup, destroy the fs and create it a new with smaller size. Then do the restore of data. But with 5.3 that's over now, so no need to focus on that.

First do a check if you have enough free PPs in the volume group:

# lsvg oravg
...
MAX LVs: 256 FREE PPs: 34 (4352 megabytes)
...

Ok we have about 4 GB. For simple unmirrored disk you can directly increase/decrease, example:

# chfs -a size=+2G /u01

This would add 2 GB to the /u01 filesystem. If you use the -2G option to the size attribute it will shrink it by 2 GB assuming there is at least 2 GB of free space. Otherwise LVM wouldn't be able to relocate the LPs. This is too simple, more fun you'll have when increasing mirrored filesystem.

My personal experience is that usually only rootvg is mirrored, so the OS is available even after disk failure. Application VGs are mirrored mostly on cluster servers. And this is still nothing complicated if you have only 2 mirrored disks in the VG because LVM can spread the mirrors only between these two disks. It's better when you have 4 disks so you have to choose the correct 2 original and the other 2 that serve as mirror. Imagine situation: 4 disks, 2 in one datacenter, 2 in other datacenter (best a few km away to be protected from local disaster =)

dc-1   dc-2
vpath2 vpath7
vpath3 vpath8

In this case it's better first increase the logical volume by desired amount of LPs and select explicitly the 2 disks that are mirrored (and that have free PPs). So we'll first increase the LV by let's say 16 partitions:

# extendlv lv_u01 16 vpath2 vpath7

Imagine you don't have enough free PPs on vpath2 and 7. What now? Well simple, just issue the extendlv command again and use the other mirrored disks. After that you can simply increase the FS and you are sure that PPs will be mirrored correctly.