Understanding the test(t) factor.

 Test factor

For an existing volume group in AIX server, if we are adding any disk to it
( Typically extending the vg), on the new disk that we add everytime in a Volume Group there will be

(size of disk in MB )/ (PP Size) = # of PPs. ( desired )

If this number is greater than the 1016 limit we will need to change the t-factor.

If the above condition is met, where you have more than 1016 PP count, then this test or t factor come into picture. Hence we need to first find out the t factor value, that we should use.


Formula for calculating factor in chvg -t:

factor * 1016 = desired # of PPs on the new disk
factor = # off PPs / 1016  ---> always round up this value.

Use the above obtained value in chvg command i.e,
#chvg -t <factor> vgname

Example:


Consider we have a VG in a AIX server with below details.

1. TOTAL PPs = 511
2. PP Size = 32 MB
3. Number of PVs = 1 and
4. The size of the disk that exists part of the volume group is 16384 MB.
5. Now i want to add a disk of size 32768 MB

• First i need to find how many PPs will be hosted on the new disk that i am adding

32768 / 32 =  1024 --> this is more than 1016 which is the limit.

• Now calculate the test(t) factor.

        factor * 1016 = 1024

        factor = 1024 / 1016 -> 1.007874016  -> If we round it up its "2" .

So use the value "2" in chvg command : "chvg -t 2 vgname"

Note: Increasing the t-factor decreases the number of PV's you can have in the volume group.