I don't have good pointers to shadow volume, other than the doc set. I don't think anything is in the Tech Tips area yet.
Basically, you could set up 2 volumes: one consisting of old storage, one w/new storage. Leave your users accessing the "old storage" volume through the ARX VIP while shadow copies to the "new storage" volume. Once the copy is complete, switch the VIP to point to the new volume. This requires 2 "cut-in" outages: once to move your clients to the VIP from the original storage, and one to flip the VIP to the new storage. (No, it will not work to have the clients access the old storage while the copy is in progress)
Nimbostratus