Replacing a mirrored root disk under VxVM is a little different from replacing any other mirrored disk under volume manager
First of all you have to confirm that your system cn boot from the mirrored disk, To ensure that run the following command out from my system is appended below (truncted for clarity)


root@baluqorcz1:/# eeprom
nvramrc=devalias vx-rootdg01 /pci@9,600000/SUNW,qlc@2/fp@0,0/disk@w2100000c50850e70,0:a
devalias vx-rootdg02 /pci@9,600000/SUNW,qlc@2/fp@0,0/disk@

You should create an alias to boot from alternate boot disk.
Once that is done, you have to remove the disk from volume manager control example
$vxdisk offline c1t0d0d0
then to physical pull the bad disk out you have remove it from OS control example
#luxadm removez-device c1t0d0s0
then you are safe to remove the disk
after that run#devfsadm -C -c disk
so that the system rereads all the drives present
then install the new drive.
After that make the OS presence of a new drive for that run this command
#luxadm insert_device c1t0d0s0
then again run this command #devfsadm -C -s disk
then bring the disk under volum manager conrol example
#vxdisk online c1t0d0s0
check that the volume manager can see it by running
#vxdisk list
now run #vxdiskadm command