Patent ID: 8600939

Claim:
A method for handling writable snapshots of an active file system, the method comprising: deleting a branch of a file system represented as a tree structure comprising a plurality of nodes each corresponding to a version of the file system, each branch beginning at an inflection point of the tree structure at which a first version of the file system was converted from an active version of the file system to a read-only version of the file system in such a way that generated second and third active versions of the file system; identifying remaining leaf nodes representing active versions of the file system, each having an associated retire file that comprises retire file entries, each retire file entry including a version identifier, a value for an earliest version value of the file system that points to a corresponding block, and a value for a latest version of the file system that points to the corresponding block, each corresponding block being of a type for which updating its latest version was deferred after a modification was made to the corresponding block; and for each retire file entry of each retire file associated with the remaining leaf nodes of the file system: deleting the retire file entry if the latest version value associated with the retire file entry indicates a read-only version of the file system; identifying a purported latest version of the file system that is earlier than that indicated by the version identifier of the retire file entry; and setting the latest version value associated with the retire file entry to the purported latest version only when the purported latest version is on the same branch of the file system as the earliest version value associated with the retire file entry.