The volume name by convention can have a max of 18 characters, one is an underscore (_) that leaves 17 characters. On the Secondary, the snapshots are named uniquely according to a specific naming convention so that it can be easily associated to the specific volumes that we may want to reattach later. The volume name uses the last seven characters of the original volume name and last 10 characters of the data volume name, separated by an underscore. This name is unique to every snapshot.
More Information
Creating synchronized snapshots using the VSS Snapshot wizard