A mechanism by which a server system executing a host application monitors utilization of a fractionally reserved space on a volume storing application data. The server system executes space reservation policies to ensure that the host application is not halted due to inability to create snapshots on the volume. In one implementation, the server system alerts a system administrator if the rate of change in the size of data snapshots exceeds a specified threshold and initiates deletion of backup datasets stored on the volume if the size of a data snapshot exceeds the available space on the volume.