Patent ID: 8250033

Claim:
A method of tracking changes to a file system subsequent to a point in time, the file system storing data in units of storage on at least one storage medium, the method comprising, in response to an operation that results in writing a first set of data to the file system subsequent to the point in time, acts of: (A) determining whether the operation results in the file system writing at least a first portion of the first set of data to at least one first unit of storage that was previously allocated to the file system and stored data for the file system, and when it is determined that the operation results in the file system writing at least the first portion of the first set of data to at least one first unit of storage that was previously allocated to the file system and stored data for the file system, performing acts of: (A1) creating a first entry in at least one map indicating that the at least one first unit of storage is being modified subsequent to the point in time; (A2) copying data stored in the at least one first unit of storage prior to the operation to at least one save volume; and (A3) writing at least the first portion of the first set of data to the at least one first unit of storage; (B) determining whether the operation results in the file system writing at least a second portion of the first set of data to at least one second unit of storage, the at least one second unit of storage being newly allocated for the operation and that did not store valid data for the file system prior to the operation, and when it is determined that the operation results in the file system writing at least the second portion of the first set of data to the at least one second unit of storage that did not store valid data for the file system, performing acts of: (B1) creating a second entry, different from the first entry, in the at least one map indicating that the at least one second unit of storage is newly allocated for the operation and is being modified subsequent to the point in time; and (B2) writing at least the second portion of the first data to the at least one second unit of storage without copying any data stored in the at least one second unit of storage to the at least one save volume; and (C) tracking changes to the file system subsequent to the point in time using the first entry and the second entry in the at least one map, wherein the first entry indicates that data related to the first entry is stored in the save volume, and wherein the second entry indicates that no data related to the second entry is stored in the save volume.