When Exchange Server is installed and the First Storage Group is created, the First Storage Group is mapped to the boot drive by default. The boot drive cannot be snapshotted. In order to implement a snapshot solution you must move the components of the First Storage Group to new volumes not on the boot drive. This involves the following procedures:
Create two new volumes, one for the mailbox store and the other for the transaction logs and system files.
Move the log, system, and database files to the appropriate new volume
See Pointing the databases and log paths to the SFW volumes.