Storage assignment is determined by reservations. Tenant administrators and business group managers can further restrict storage volume assignment by specifying a single datastore or a storage reservation policy that represents multiple datastores to a volume. With the multi-storage feature you can assign the volumes of a virtual machine to different datastores for the vSphere, KVM (RHEV), and SCVMM platforms.
When you assign the volumes of a virtual machine to different datastores, you can control and use storage space more effectively. For example, you might deploy the operating system volume to a slower, less expensive datastore and the database volume to a faster datastore.
You can assign a single datastore or a storage reservation policy that represents multiple datastores to a volume. When you assign a single datastore to a volume, that datastore is used at provisioning time, if possible. When you assign a storage reservation policy to a volume, one of its datastores is used at provisioning time.
A storage reservation policy is a tag applied to one or more datastores by a fabric administrator and is used to group datastores that have similar characteristics, such as speed or price. A datastore can be assigned to only one storage reservation policy at a time, but a storage reservation policy can have many different datastores. A fabric administrator creates a storage reservation policy and assigns it to one or more datastores. A tenant administrator or business group manager then assigns the storage reservation policy to a volume in a virtual blueprint. When a user requests a virtual machine that uses the blueprint, the storage reservation policy specified in the blueprint is used to select a datastore for the machine’s volume.
When you add or edit a volume in a virtual blueprint, you can make the following assignments:
Assign a single datastore to the volume. This one-to-one relationship assigns only the specified datastore at provisioning time. If the datastore is not available or lacks sufficient space, provisioning fails.
Assign a storage reservation policy to the volume. This assignment allows the selection of one of the datastores associated with the storage reservation policy at provisioning time. If the policy’s datastores are unavailable or lack sufficient space, provisioning fails.
Assign a storage reservation policy to the volume and include the custom property VirtualMachine.DiskN.StorageReservationPolicyMode with the value of NonExact. This configuration allows you to assign a datastore that is not included in the storage reservation policy.
Do not assign a datastore or a storage reservation policy to a volume. Not making an assignment allows selection from all available datastores at provisioning time. Provisioning fails if a datastore with sufficient space is not available.
Datastore priority, as assigned by a datastore reservation, is also used to select a datastore at provisioning time.
Avoid specifying a storage path and a storage reservation policy for the same volume. If you must specify a storage path and a storage reservation policy for the same volume, the storage path takes precedence over the storage reservation policy.