The reason for asking is because we use SAN boot, we have rootvg on one disk on our production site and another disk for rootvg on our DR site - these are mirrored at LVM level (so lg_dumplv is not...
If all else fails you could always assign a new 300GB LUN to the VG, use migratepv to migrate from original disk to new and then you can take the original disk away (after doing reducevg of course).
I went through this a while ago, if I remember correctly you can just install sddpcm and then reboot. The above commands you have posted are if you are upgrading sddpcm to another OS release - if you...