Friday, August 10, 2012

Breaking limits of LVM, Physical Partitions, Volume Groups in AIX

Are you facing the situation that you can not extend LUN or mirror smaller LUNs to one big LUN in AIX because you reached limit of Physical Partitions in Volume Group?

extendvg VGname hdisk4
      0516-1254 extendvg: Changing the PVID in the ODM.
      0516-1162 extendvg: Warning, The Physical Partition Size of 512 requires the
              creation of 1140 partitions for hdisk4.  The limitation for volume group
              VGname is 1016 physical partitions per physical volume.  Use chvg command
              with -t option to attempt to change the maximum Physical Partitions per
              Physical volume for this volume group.

Is yes, read more :-)

AIX LVM limitation:

VG typeMax PVsMax LVsMax PPs per VGMax PP sizeMax PPs per PV
Normal VG3225632,512 (1016 * 32)1 GB1016
Big VG128512130,048 (1016 * 128)1 GB1016
Scalable VG102440962,097,152128 GBNone

There are two solutions:

A) Converting VG to scalable VG

- VG must be varied off
- Convert VG to scalalabe
- VG must then be varied on

varyofffvg VGname
chvg -G VGname
varyonvg  VGname

B) Changing VG factor

- VG can be online
- Change VG factor to number between 2 - 16

chvg -t 2 VGname
      0516-1164 chvg: Volume group VGnamechanged.  With given characteristics VGname
            can include up to 16 physical volumes with 2032 physical partitions each.

Source: IBM Support page

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