This indicates the storage type of this row. It tells the router whether this VC configuration row should survive a reboot, nonVolatile, or vanish and need reprovisioning after a restart, volatile, which matters when deciding whether a temporary test pseudowire needs to be manually cleaned up or will simply disappear on its own. For example, setting this to volatile on a short-lived test pseudowire lets it automatically disappear on the next router reboot without requiring the admin to remember to manually remove the configuration afterward.