Can you assign new disk without removing old ones ?
Hmm funny why do you need 2 disks assigned from SAN storage
when you are not mirroring the data ?
Another problem is that this is not supported version of VIO serer
I strongly advice to upgrade to more supported version
First small checking paste output of commands
1 .go to privileged mode - because you are probably o padmin user
to gain root access run command oem_setup_env
2. Information about disks sizes bootinfo -s hdisk0; bootinfo -s hdisk2
3. volume group information lsvg rootg
4. check whats on disks lspv -l hdisk0; lspv -l hdisk2
After this you will see if you need 2 disks or just one of them
Before you will start any disruptive commends make mksysb image if you do not know how (simtty mksysb)
To move data to new disks
1. Assign new disks to VIO server
2. Run Config Manager to discover them in system (cfgmgr)
3. Extend the volumegroup extendvg rootvg new_disks
4. Mirror data to new disks (mirrorvg -s -c2 rootvg new_disks_names)
5. Sync data between mirrors (syncvg -P 32 -v rootvg)
6. Remove copy from old disks (unmirrorvg -c1 rootvg hdisk0 hdisk2)
7. Remove old disks from volume group (reducevg rootvg hdisk0 hdisk2)
8. recreate bootimages bosboot -a
9. update bootloader bootlist
Easy