A storage system permits virtual storage of user data by implementing a logical
disk mapping structure that provides access to user data stored on physical storage
media and methods for generating point-in-time copies, or snapshots, of logical
disks. A snapshot logical disk is referred to as a predecessor logical disk and
the original logical disk is referred to as a successor logical disk. Creating
a snapshot involves creating predecessor logical disk mapping data structures and
populating the data structures with metadata that maps the predecessor logical
disk to the user data stored on physical media. Logical disks include metadata
that indicates whether user information is shared between logical disks. Multiple
generations of snapshots may be created, and user data may be shared between these
generations. Methods are disclosed for maintaining data accuracy when write I/O
operations are directed to a logical disk.
