1. A method for storage allocation and reclamation in a storage device, comprising: executing a distributed computer system having a plurality of file systems accessing storage on a shared storage device; creating a physical storage allocation state map that indicates whether a plurality of data blocks comprising a range of data is allocated or unallocated; consulting a free extent state map to identify free data blocks of the shared storage device; performing an allocation operation causing the shared storage device to allocate storage a requested range of allocation; updating the physical storage allocation state map in accordance with the requested range of allocation; upon a subsequent reclamation process, accessing the physical storage allocation state map to identify free previously allocated data blocks; and performing reclamation processing on the identified free previously allocated data blocks.