US Patent 7739241 Implementing dynamic copy-on-write (COW) storage compression through purge function

Methods, apparatus and computer program product implement enhanced dynamic copy-on-write storage compression. For a write operation, a purge function for a block being written is detected by the COW storage for compressing freed blocks from the COW storage. Responsive to the detected purge function and the block being a previously written block in the COW storage, the previously written block in the COW storage is deleted from the COW storage. Responsive to the detected purge function and the block not being a previously written block in the COW storage, the block is marked as zero in the COW storage.