Assuming that you also want to create full-sized snapshots of application volumes in mypool that can be moved into a different disk group, the following command creates a clone storage pool, myclpool, in the same disk group as mypool:
# vxpool -g mydg create myclpool \
dm=mydg09,mydg10,mydg11,mydg12 \
autogrow=pool pooldefinition=mirrored_volumes
This pool supports the creation of mirrored volumes. It also has a non-default autogrow policy that prevents it aggregating disks from the disk group outside the pool.
See Preparing storage pools for full-sized instant snapshots.