A storage monitoring system may reside between a file system and a storage system in a thin provisioned storage system. The storage monitoring system may create space holder files within a volume, where the space holder files contain an address space not backed up with physical storage. As requests for storage space are received from a file system, the storage monitoring system may allocate physical space to the volume by provisioning portions of the physical storage device to the volume and by removing one of the space holder files. The storage monitoring system may present alerts when physical storage space is low, as well as return an amount of physical space available to a volume size request.