How To Create Volume Group

April 22nd, 2009

Lots of things need to be considered while creating Volume Groups. In this post I’m presenting various scenarios of Volume Group creation. In the previous post I introduced you to listing of Volume Groups. For the ones interested in fundamentals of Logical Volume Manager read the previous article: Aix Logical Volume Manager A Brief Introduction

To add a Volume Group, we need to have few things in mind:

  1. The name of Volume Group.
  2. Whether you want to limit the maximum number of Physical Volumes in this Volume Group.
  3. Names of Physical Volumes used while creating Volume Group.
  4. The size of Physical Partition.

I assume the size of all Physical Volumes to be hdisk2 and hdisk3 each of size 130GB.

How To Create A Volume Group
If you want to keep default settings the Physical Partition size will be: 130*1000/1016 MB which turns about to be around 128MB.

So, you VG creation command will be:
mkvg -y my_vg hdisk2 hdisk3

How To Create A Volume Group With More Than 1016 Physical Partitions Per Physical Volume
Now, let’s say you want to have maximum number of Physical Partitions to be more than 1016 or you want lower than 128MB Physical Partition size, you can use t-factor. The t-factor helps you increase the maximum number of Physical Partitions per Physical Volume. But it decreases the maximum possible Physical Volume in a Volume Group. If you could have 32 Pvs previously, with a t-factor of 2, you will have now maximum of 16 Pvs. T-factor can only be an integer.

Now see what happens:

Maximum no. of PPs: 2*1016=2032
Size of PV: 130GB.
Size of single PP:130*1000/2032=64MB

So, you will need to specify s also, which stands for the size of Physical Partition to use. Which in our case will be 64MB.

mkvg -s 64 -t 2 -y my_vg hdisk2 hdisk3

How To Create A Big Volume Group
To create a Big Volume Group, specify -B option. With this option you can have maximum of 128 Physical Volumes and 512 Logical Volumes.
Issue the command:
mkvg -B -v 512 -y my_vg hdisk2 hdisk3

-v option is used to specify the number of Logical Volumes. The valid values of -v are: 256, 512, 1024 and 2048.

How To Create A Scalable Volume Group
To create a Scalable Volume Group, specify -S option. With this option you can have maximum of 1016 Physical Volumes and 2048 Logical Volumes.
Issue the command:
mkvg -S -v 2048 -y my_vg hdisk2 hdisk3

How To Create A Volume Group With A Given Major Number
Let’s say for example you want to create a Volume Group with a Major Number 43.
Issue the command:
mkvg -V 43 -y my_vg hdisk2 hdisk3

To know the major number, you should issue the command:
wiw_labs:$ lvlstmajor
43…

How To Create A Volume Group And Accept Physical Volumes From Standard Input
To accept list of Physical Volume from standard input you need to issue mkvg command with -i option.
echo “hdisk2 hdisk3″ | mkvg -i -y my_vg

How To Create An Enhanced Concurrent Capable Volume Group

For enhanced concurrent capable Volume Group you need to issue mkvg command with -c option. See this article for more information on types of Volume Group. .

mkvg -c -y my_vg hdisk2 hdisk3

If you are using HACMP then use:
mkvg -C -y my_vg hdisk2 hdisk3

How To Create A Volume Group Which Does Not Vary on Automatically
For creating a Volume Group which does not varyon automatically, you need to issue mkvg command with -n option.
mkvg -n -y my_vg hdisk2 hdisk3

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