First of all you need to add the LUN to the disk group

# vxdisksetup -if <disk name>   --> This will initialize the disk. Basically it will put private and public region on the disk header so that volume manager can work with the disk.
# vxdg -g <disk group name> adddisk <disk access name, as you prefer>=<disk media name, as displayed in "vxdisk list" command>

This command would increase the volume size as well as file system size
# vxresize -g <disk group name> -F vxfs <volume name> <specify new volume size>

FYI. VM4.0 is no longer supported, unless you have support exception, so I suggest you to go for an upgrade if it is an important server.

Hi Dev,

Thank you for giving reply.

1)  My exisiting volume group is currently mounted, can i increase the size while disk group is mounted? this is in production
2)  Is there any exstra steps to be involved for existing 2 node cluster and make the LUN cluster aware?

Pl. guide me

 In a cluster setup,  first you need to make sure the LUNs are available/ visible  on both the nodes. 

Then perform vxdisksetup to match the format (sliced / simple / or cds) 
add luns to the shared diskgroup. Once the luns are successfully added to the diskgroup, simple vxresize command will magically expand the filesystem for you.

You can increase the mounted shared veritas  filesystem, provided you see the LUNs from both the nodes without any hitch. 

good luck.

Thank you for your suggession

While resize i am getting following error msg.

# /usr/lib/vxvm/bin/vxresize -g databkp_dg -F vxfs databkp_dg02 +300g
VxVM vxprint ERROR V-5-1-2716 Record databkp_dg02 found but object type not selected
VxVM vxresize ERROR V-5-1-4705 Problem running vxprint command for volume databkp_dg02, in diskgroup databkp_dg

Please suggest

Pl. ignore my previous error msg.

Solved the problem, thank u very much for your support Mr. Dev and Mr. Jayess