Patent ID: 6944732

Claim:
A method to support snapshots in a storage area network (SAN) providing a plurality of clients with concurrent direct I/O access to a file in the SAN, wherein the SAN uses an access unit protocol for file system access, said method comprising operating a file server to: start to maintain, at a time T 1 , a time T 1 snapshot volume of a live volume of data in the file system; receive, from a client C 1 , at a time subsequent to T 1 , an update access request for a portion of a file that includes data stored in access unit B 1 of the live volume; responsive to the update access request, allocate, to the time T 1 snapshot volume, a new access unit B 2 corresponding to access unit B 1 , and copy data stored in access unit B 1 to access unit B 2 ; and move, responsive to data being copied into access unit B 2 , access permissions for a client C 2 so that client C 2 accesses data from access unit B 2 instead of access unit B 1 .