Unspecified

Uses the default snapshot type of the VSS provider.

Differential

Uses a copy-on-write type of snapshot. For example, to back up an EMC CLARiiON array with an EMC CLARiiON SnapView Snapshot, select Differential.

Plex

Uses a clone snapshot or mirror snapshot. For example, to back up an HP EVA array with an HP EVA Snapclone snapshot, select Plex.