US Patent 8966198 Providing snapshots of virtual storage devices

In general, one aspect of the subject matter described in this specification can be embodied in methods that include receiving, at a computer system, a request to create a snapshot of a virtual storage device, wherein the virtual storage device virtually stores data at virtual addresses, the data being physically stored at a plurality of physical storage locations that are managed by an underlying storage system associated with virtual storage device; the methods can further include identifying, by the computer system, one or more regions of the virtual storage device that have been written to since a previous snapshot of the virtual storage device was created; the methods can additionally include generating a unique identifier for the requested snapshot; and creating the requested snapshot using the identified one more regions and the unique identifier.