Patent ID: 7035881

Claim:
A computer-implemented method of operating a file server said method comprising the steps of: creating and maintaining, in computer data storage, a read-write snapshot copy of a production file system, the read-write snapshot copy of the production file system being created and maintained by: a) creating a read-only snapshot copy of the production file system; and b) creating a read-write snapshot copy of the production file system based on the read-only snapshot copy of the production file system, and maintaining the read-write snapshot copy of the production file system by maintaining a set of save volume blocks of new data of the read-write snapshot copy of the production file system, and (i) writing to a first specified block of the read-write snapshot copy of the production file system by writing to a respective save volume block allocated to the first specified block of the read-write snapshot copy of the production file system, (ii) reading from a second specified block of the read-write snapshot copy of the production file system by checking whether there is a respective save volume block allocated to the second specified block of the read-write snapshot copy of the production file system, and upon finding that there is a respective save volume block allocated to the second specified block of the read-write snapshot copy of the production file system, reading from the respective save volume block found to be allocated to the second specified block of the read-write snapshot copy of the production file system, and (iii) reading from a third specified block of the read-write snapshot copy of the production file system by checking whether there is a respective save volume block allocated to the third specified block of the read-write snapshot copy of the production file system, and upon finding that there is not a respective save volume block allocated to the third specified block of the read-write snapshot copy of the production file system, reading the third specified block of the read-write snapshot copy of the production file system by reading from the read-only snapshot copy of the production file system.