The following are the requirements for creating a vault:
A robot may contain multiple vaults, but a vault cannot span robots. Therefore, if you configured three TLD robots for Vault (not connected with pass-through devices), you must define at least three logical vaults, one for each TLD robot.
Volumes in a vault must have the same density. If a robot has volumes of different density and you want to use all of those volumes for Vault, that robot must have a separate vault for each volume density.