Conversion of Normal VG to Big VG

1      Introduction

1) What is the need for this conversion?

       Whenever the total number of PVs in a Normal VG reaches max PV limit (32 PVs/VG), we can not add new PVs in the VG. But if we convert the Normal VG to Big VG Format, we can accommodate 128 PVs in a single VG.

2      How to Convert the VG Format?

What are the pre-requisites?

While converting a  Normal VG to Big VG format, the VGDA gets expanded.

So we need at least 1 free PP per PV in all the PV residing in the VG. If not we have to follow the following method to move date from the used PPs from a PV to an unused PP in another PV.

How to move PPs across PVs?

Use the below command to view the current PVs in the VG and Total/Free PPs per PV.

$ lsvg -p vg000

vg000:

PV_NAME    PV STATE    TOTAL PPs   FREE PPs    FREE DISTRIBUTION

vpath1             active               595               594             118..119..119..119..119

vpath2                         active               595               247             09..00..00..119..119

vpath0             active               595                 0               00..00..00..00..00

vpath3             active               595                 0                00..00..00..00..00

Here vpath0 and vpath3 don’t have any free PPs. In this case, we should move 1 used PP from both the PV to some unused PP in vpath1 or vpath2.

Before moving, please collect the below information.

VGID              :           You can get this info from lsvg command.

Source PVID  :           You can get this info from lspv <pv_name>

Source PP No. :           This PP should be an used PP from the source PV.

                                    You can get this info from lspv –M <pv_name>

Target PVID   :           You can get this info from lspv <pv_name>

Target PP No. :           This PP should be an unused PP from the Target PV.

You can get this info from lspv –M <pv_name>

After the collection of the above details, use the below command to migrate the data from unused PP to used PP.

lmigratepp -g VGid -p SourcePVid -n SourcePPnumber 

-P DestinationPVid -N DestinationPPnumber

After achieving the pre-requisites, check the OS version.

For AIX Version 5.1, use Method 1 to convert the VG to Big format.

For AIX Version 5.2 and above, use Method 2 to convert the VG to Big format.

Method 1:

1. Arrange for the outage for this VG.
2. During outage execute the below mentioned commands:
1. umount all the file systems belonging to the VG.
2. Run `chvg –B <vg_name>`.

This command takes bit long time since it expands the VGDA for all the PVs belonging to this VG.

Method 2:

1. Run `chvg –B <vg_name>`.

This command takes bit long time since it expands the VGDA for all the PVs belonging to this VG.

3      Check the result

Run `lsvg <vg_name>` and verify the Max PVs Field. It should be 128 for a Big VG.

$ lsvg vg000

VOLUME GROUP:             vg000              VG IDENTIFIER:  00597f2a068e49c0

VG STATE:                          active               PP SIZE:        8 megabyte(s)

VG PERMISSION:               read/write        TOTAL PPs:      2380 (19040 megabytes)

MAX LVs:                            256                   FREE PPs:       841 (6728 megabytes)

LVs:                                       2                       USED PPs:       1539 (12312 megabytes)

OPEN LVs:                           2                       QUORUM:         3

TOTAL PVs:                         128                   VG DESCRIPTORS: 128

STALE PVs:                          0                      STALE PPs:      0

ACTIVE PVs:                       128                   AUTO ON:        yes

MAX PPs per PV:                1016                 MAX PVs:        128