Find disks in AIX volume groups that are bigger than supported by VG
brian_s 270002K5X3 Visits (6775)
If you work with AIX systems that have original or big volume groups you are going to have limitations on the size of LUN's that can be supported by the volume group.
To find the maximum disk size allowed in the volume group, run "lsvg <vgname>". Find the "PP Size" and multiply it by the "MAX PPs Per PV". For example, if your PP size is 16 MB and your Max PPs Per PV is 2032 the maximum PV/disk size would be 32,512 MB (about 32 GB).
But what happens in this scenario if you take a 20 GB LUN and increase its size on the SAN to 300 GB? (way past the 32 GB limit of this particular volume group). AIX will not allow the LUN to increase in size when you run the "chvg -g" command, and the extra space will not be available to you. The extra space is allocated on the SAN but not usable on AIX so the space is essentially wasted.
Now, to fix this you have two options. Depending on the situation you might be able to change the volume groups "Factor Size" (see my previous post on Deci
How can you tell if you have LUN's that are bigger than what the volume group supports? One of the easiest ways is to compare the output of what "lspv <hdisk>" reports for the total size of the disk against what "bootinfo -s" reports as the size of the disk. Normally there is a small discrepancy between these sizes because of the overhead that the volume group takes, but if there is a big discrepancy it means either the disk is to large for the volume group to support it, or you haven't run "chvg -g" yet for the volume group to recognize the increase size of the hdisk.
Here is a one liner script that will check all of the hdisks on a server. The first column of the output is the size of the disk that "lspv" reports. The second column is the size that "bootinfo -s" reports. The third column is the difference between these two numbers.
As you can see in this example, someone tried to resize hdisk5 to 300 GB, however this particular volume group only supports a max PV/hdisk size of 32 GB so the extra space cannot be utilized unless the volume group factor size is changed (which may or may not be possible) or unless the volume group is converted to a big or scalable volume group.