Patent ID: 8190570

Claim:
A computer implemented method of looking up a child directory in a virtual file system, the method comprising: detecting, by a backup data processing system, a changeover from a primary data processing system to the backup data processing system; responsive to detecting the changeover, reconstructing the virtual file system in the backup data processing system from data describing the virtual file system stored in a storage device to form a reconstructed virtual file system, wherein the data describing the virtual file system is received from the primary data processing system, wherein reconstructing the virtual file system comprises: responsive to determining a name of the directory and a name of a child directory, determining whether the child directory exists in the reconstructed virtual file system as a child of the directory, wherein the child directory exists if it is constructed from the data describing the virtual file system; and responsive to a determination that the child directory exists in the reconstructed virtual file system as a child of the directory, returning the child directory to form a found child directory and storing the found child directory in the storage device.