Patent attributes
Described is a technology by which a secondary nonvolatile storage (e.g., a flash memory device) maintains a copy of the changes made to a hard drive after a data backup operation. The backup changes are combinable with backed up data to recreate a hard drive state, whereby changes after the last backup are not lost, e.g., if the hard drive fails. The backup change data may maintain the changes at the block (e.g., allocation unit) level corresponding to hard drive blocks, or at the file level, corresponding to files or parts of files on the hard drive. The backup changes may be filtered, so that only certain data (e.g., user data) are maintained as backup change data. Read requests can be satisfied by reading data from the backup change data, or from a performance (e.g., disk) cache that may also reside on the nonvolatile storage.
