Originally posted by: adam7764

Hi, im new to AIX and need some help understanding the concept of why you would need to increase the size of a logical volume.

When a filesystem is full i increase it using chfs command and everything is good. So what is the difference between chfs and extendlv?

Are they in affect doing the same thing?

Thanks

Originally posted by: GarlandJoseph

No there are not the same.  You  might think of them as containers, both dealing with file/disk types of resources.   Logical volumes allow you to do things like control the place of where they are on disks.   Filesystems have concepts such as filesytem type (ext, jfs, jfs2).  For an example of the differences, see the man pages for command involving logical volumes and filesystems.  This will give you insight into the differences.   You may also what to familiarize yourself with LVM (volume group mangement).

Originally posted by: adam7764

Thanks for your reply Joseph.

My main confusion is really related to the size. For example i have a logical volume that is 128 mb and has 18 pp's (total of 2.3 g). When i look at the filesystem for this lv it  has  4718592 512byte units (total of 2.3g). So there both the same size. If i increase the filesystem using chfs by 128mb or if i increase the lv to 19 pp's is this not doing the same thing?

Thanks

Originally posted by: Wouter Liefting

chfs will, under the covers, call lvextend for you. So when you call chfs, lvextend will first extend the LV (the "container" if you wish), and then chfs will increase the filesystem size.

In contrast, if you call lvextend, it will not call chfs for you. So you only increase the LV, but not the filesystem.

lvextend is only useful for LVs that do not contain a JFS/JFS2 filesystem, and even then it's probably not much use in isolation: You would need an appropriate command to extend whatever structure is to be found inside the LV, to the new size of the LV.

For LVs that contain a JFS/JFS2 filesystem you should nearly always use chfs.

Originally posted by: adam7764

Hi Wouter Liefting, thankyou for your explanation, that makes perfect sense and has cleared up my confusion.