Posts Tagged ‘Volume Group’

The mkvg FAQs

Thursday, April 23rd, 2009

Here in this post I’m presenting few things in the form of FAQs. The can be used as a ready reference while creating Volume Groups. To know how to create Volume Group read the article: How To Create Volume Group.

Q 1. While creating Volume Group can I use Physical Volumes which are part of other Volume Groups?
Answer: No and Yes.
No: The Physical Volumes specified are checked to see if these are part of other Volume Groups. If they are used in other Volume Groups, the command terminates without creating Volume Group.
Yes: If you specify -f option while creating a new Volume Group, then its possible. See what happens.
Let’s say you have issued the following command:
mkvg -f -y my_vg hdisk2 hdisk3 hdisk4

Let’s say hdisk3 is part of another Volume Group: my_other_vg. Here two things happen:

  1. If the Volume Group: my_other_vg is varied off at the time of creating new Volume Group my_vg, the Volume Group my_vg will be created with the Physical Volumes hdisk2, hdisk3 and hdisk4. But, the previous contents of hdisk3 will be lost.
  2. If the Volume Group: my_other_vg is varied on, the command will terminate and Volume Group my_vg will not be created.

Q2. Which users can create a Volume Group?
Answer: The user should be either root or someone belonging to System group.

Q3. Is it necessary to specify the Physical Partition size while creating Volume Group?
Answer: Obviously No. The mkvg command automatically adjusts the size of Physical Partitions according to the size of Physical Volume. If however you need to specify the size of Physical Partitions, then keep in mind that it should be large enough to accommodate the full Physical Volume.

For example: if suppose you have physical volume of size 130GB the Physical Partitions size is automatically adjusted to 128MB by the system. If you need to change it to 64MB, then specify -s 64 and -t 2. See this article: How To Create Volume Group to know more.

Q4. How can I specify the Physical Partitions size less than the default size?
Answer: Refer to Q3.

Q5. While creating Volume Group can I use Physical Volumes which are part of third party Volume Managers?
Answer: No: The command terminates if it detects that the Physical Volume specified is being used by some other third party Volume Manager e.g VxVM(Veritas Volume Manager).

Q6. How can I use the Physical Volume in Volume Group creation which was in use of some other third party Volume Manager?
Answer: You have to clear the Physical Volume of the third party volume manager. Specify -C option with chpv as below:
chpv -C hdisk3

Q7. Does Volume Group varyon always automatically?
Answer: No. By default the Volume Group varies on automatically after creation.
In following two conditions, the Volume Group will not varyon automatically:

  1. If you specify -n option with mkvg command.
  2. If you specify -C option, to make it concurrent capable, then it’s not varied on automatically

Q8. Can I specify total number of Physical Partitions in Volume Group at the time of creation?
Answer: Yes. You can use -P option. The valid values are: 32, 64, 128, 256, 512, 1024, 2048. Specifying any value will limit maximum number of physical partitions to: valueX1024 partitions. e.g 32 will limit maximum number of physical partitions in Volume Group to : 32X1024=32768 partitions.

Q9. Can I specify total number of Logical Volumes in Volume Group at the time of creation?
Answer: Yes. You can use -v option. The valid values are: 256, 512, 1024, 2048. Specifying any value will limit maximum number of Logical Volumes in Volume Group to : value Logical Volumes. e.g 512 will limit maximum number of Logical Volumes in Volume Group to : 512 Logical Volumes.

Q10. Can I import Volume Group created in AIX 5.3 to AIX 5.2 or lower?
Answer: By default No. But if you want to do it, specifying -I option at the time of creation of Volume Group, you will be able to import in AIX 5.2 or lower.

Q11. Are there any conditions when I can not import Volume Groups created in AIX 5.3 to lower versions of AIX?
Answer: Yes. In the following two conditions:

  1. If Volume Group is Big VG, created with -B flag then you can not import it to AIX 4.3.1 or lower.
  2. If Volume Group is Scalable VG, created with -S flag then you can not import it to AIX 5.2 or lower.

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