A method for a file server to support snapshots in a storage area network (SAN) providing a plurality of clients with concurrent direct I/O access to a file system in the SAN, in which the SAN uses an access protocol for file system access. The method includes operating the file server to: start to maintain, at a time T1, a time T1 snapshot volume of a live volume of data in the file system; receive, from a client C1 at a time subsequent to T1, an update access request for a portion of a file that includes data stored in access unit B1 of the live volume subsequent to time T1; and responsive to the update access request, allocate, to the time T1 snapshot volume, a new access unit B2 corresponding to access unit B1, and copy data stored in access unit B1 to access unit B2.