Determining PP sizes when creating AIX Volume Groups
brian_s 270002K5X3 Comment (1) Visits (14404)
The man page for the AIX mkvg command states this about how Physical Partition sizes are determined for volume groups when they are created:
The default value for PP size is kind of hard to understand based on the man page description. Below are a couple of tables that show given a hdisk size what the default PP size would be if a volume group was created on it without specifying a PP size.
AIX basically defaults to the smallest PP size possible for the given disk, which is almost certainly not what you want. Especially with original and big volume groups a small PP size puts severe limitations on the total capacity of the PV and volume group.
I recommend using scalable volume groups, and specifying a PP size rather than just taking the default value. Think about what the requirements will be in the future, and pick a PP size for the volume group based on that. Remember that the PP size determines the increments that you will be able to add space to filesystems to, so don't pick too large of a PP size. For example, if you pick a 1 GB (1024 MB) PP size, and have a 4 GB filesystem and you need to add 0.5 GB to, you will be forced to add a full 1 GB since that is the PP size and you would have to add a entire PP. If the PP size had been 512 MB you would have been able to add just 0.5 GB rather than being forced to add a full GB.
To allow the volume group to have the maximum overall capacity in the future for growth, pick the largest PP size that would work for your current and future requirements. 128 MB, 256 MB, and 512 MB PP sizes are good middle ground sizes that will work in most circumstances (again, pick the largest that will work for your environment). Remember that you can not change a volume groups PP size after it is created without backing the data up and recreating it.
Here are the default PP sizes that AIX will default to if you don't specify the PP size yourself: