Brian Smith's AIX / UNIX / Linux / Open Source blog
Matching: storage X
|Modified on by brian_s|
Modern versions of AIX have three types of Volume Groups: Original, Big, and Scalable.
In my opinion, for any new volume groups you are creating you should always use scalable unless you will have the need to export the volume group and import it on very old versions of AIX. Scalable volume groups have very few limitations when compared to big and original volume groups.
Unfortunately there are a ton of original and big volume groups out there in the world, and it can be very tricky to understand their limitations. The main barriers people hit with original and big volume groups is the limit on the maximum number of disks in the volume group ("MAX PVs") and the limit on how many PP's can be on the disk which directly impacts how large a disk in the volume group can be ("MAX PPs per PV").
To further complicate this, these 2 limitations are variable based on the volume group "Factor". The factor is a number between 1-16 for original volume groups, and between 1-64 for big volume groups. As you increase the factor, the "MAX PVs" does down and the "MAX PPs per PV" goes up. It is essentially a trade off: if you would like larger disks, you can't have as many. If you want more disks, they can't have as many PP's on them.
The factor of a volume group can be changed with the "chvg -t" command.
Below is how the factor affects original VG's and Big VG's (Scalable VG's don't have a factor setting):
The standard AIX utilities such as "lsvg" don't directly show you the volume group type or the volume group factor. There is a "readvgda" command that you can run on a hdisk (i.e. "readvgda hdisk0") that will show the volume group type and the factor, but it also shows a bunch of other info so its difficult to quickly and efficiently get information from.
I've written a script that produces a quick report showing several things such as the volume group type, factor size, max PV's, used PV's, Max PP's per PV, PP Size, and max disk size.
Here is a screenshot of the report produced:
Here is the script: