How To
Summary
This Technote is about the different Values of Volume Group Factor and how to calculate the required Factor based on the number of disks ((Max PVs)) and number of PPs on each disk, ((Max PPs per PV)) that you need.
Steps
The two common barriers people hit with Small and Big volume groups is the limit on the maximum number of disks in the volume group ("MAX PVs") and the limit on how many PPs can be on the disk which directly impacts how large a disk in the volume group can be ("MAX PPs per PV").
By default A Small VG is limited to 32512 physical partitions. (32 physical volumes, each with 1016 partitions) and Big VG is limited to 130048 physical partitions. (128 physical volumes, each with 1016 partitions) these limitation can prevent you from adding a big disk to your VG if your PP size is small, however you can change this limit with: chvg -t or in other words change the factor.
Let's say that you have a Small VG and you want to extend it with a PV with of size :- 200 GB
And you have a PP size of :- 128 MB
If we want to calculate the Number of PPs that this PV will be divided to it will be :- 204,800 MB/128MB = 1600 PPs. Given that the limit of 1016 is smaller than 1600, this PV will not be added to the VG. So how can we solve this limitation?
Small and Big VG
|
Factor |
Max PVs for Small VG |
Max PVs for
Big VG
|
Max PPs per PV |
|
1 |
32 |
128 |
1016 |
|
2 |
16 |
64 |
2032 |
|
3 |
10 |
42 |
3048 |
|
4 |
8 |
32 |
4064 |
|
5 |
6 |
25 |
5080 |
|
6 |
5 |
21 |
6096 |
|
7 |
4 |
18 |
7112 |
|
8 |
4 |
16 |
8128 |
|
9 |
3 |
14 |
9144 |
|
10 |
3 |
12 |
10160 |
|
11 |
2 |
11 |
11176 |
|
12 |
2 |
10 |
12192 |
|
13 |
2 |
9 |
13208 |
|
14 |
2 |
9 |
14224 |
|
15 |
2 |
8 |
15240 |
|
16 |
2 |
8 |
16256 |
|
for Big VG only |
|||
|
Factor |
Max PVs for
Big VG
|
Max PPs per PV |
|
|
17 |
7 |
17272 |
|
|
18 |
7 |
18288 |
|
|
19 |
6 |
19304 |
|
|
20 |
6 |
20320 |
|
|
21 |
6 |
21336 |
|
|
22 |
5 |
22352 |
|
|
23 |
5 |
23368 |
|
|
24 |
5 |
24384 |
|
|
25 |
5 |
25400 |
|
|
26 |
4 |
26416 |
|
|
27 |
4 |
27432 |
|
|
28 |
4 |
28448 |
|
|
29 |
4 |
29464 |
|
|
30 |
4 |
30480 |
|
|
31 |
4 |
31496 |
|
|
32 |
4 |
32512 |
|
|
33 |
3 |
33528 |
|
|
34 |
3 |
34544 |
|
|
35 |
3 |
35560 |
|
|
36 |
3 |
36576 |
|
|
37 |
3 |
37592 |
|
|
38 |
3 |
38608 |
|
|
39 |
3 |
39624 |
|
|
40 |
3 |
40640 |
|
|
41 |
3 |
41656 |
|
|
42 |
3 |
42672 |
|
|
43 |
2 |
43688 |
|
|
44 |
2 |
44704 |
|
|
45 |
2 |
45720 |
|
|
46 |
2 |
46736 |
|
|
47 |
2 |
47752 |
|
|
48 |
2 |
48768 |
|
|
49 |
2 |
49784 |
|
|
50 |
2 |
50800 |
|
|
51 |
2 |
51816 |
|
|
52 |
2 |
52832 |
|
|
53 |
2 |
53848 |
|
|
54 |
2 |
54864 |
|
|
55 |
2 |
55880 |
|
|
56 |
2 |
56896 |
|
|
57 |
2 |
57912 |
|
|
58 |
2 |
58928 |
|
|
59 |
2 |
59944 |
|
|
60 |
2 |
60960 |
|
|
61 |
2 |
61976 |
|
|
62 |
2 |
62992 |
|
|
63 |
2 |
64008 |
|
|
64 |
2 |
65024 |
|
The factor of a volume group can be changed with the "chvg -t" command.
How to know my Current VG factor :-
Factor = Max PPs per PV/1016 (where Max PPs per PV can be found by lsvg vgname)
How to calculate the factor value that I require :-
1 - Identify new disk size
2 - Identify the PP size defined for the VG
3 - First you will have to find :- Number of pps on the new disk that you want to add
Number of pps on the new disk = disk size (PV) / your VG (PP) size (make sure your unit is the same)
In our previous example :- 204,800 MB /128 MB = 1600
4 - Factor value = Number of pp’s on the new disk / 1016
Factor value = 1600 / 1016 = 1.5 we take this value to the next available value which is = 2
Required t - Factor value here = 2
This will limit the Max PVs in the VG to 16, and increase the Max PPs per PV to 2032 PP which is more than the required 1600 PP
In this case we will run the command
#chvg -t <factor> vgname
#chvg -t 2 vgname
Document Location
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Document Information
Modified date:
26 September 2021
UID
ibm16372976