Delegated reference count base file versioning

A method of operating a network file server having a network adapter coupling the network file server to a data network of client computers;

• data storage storing files, and a data processor coupled to the data storage and the network adapter for access of the client computers to the files stored in the data storage, the files in the data storage being organized as a hierarchy including inodes, intermediate nodes, and data blocks, the files stored in the data storage including a production file having a first intermediate node in the hierarchy, the first intermediate node being a descendant of the production file inode in the hierarchy, said method comprising:
• storing in the data storage a reference count for the first intermediate node, and storing in the data storage a delegated reference count for the relationship of the production file inode and the first intermediate node,
• the data processor creating in the data storage a snapshot copy of the production file by allocating a snapshot copy inode and sharing the first intermediate node between the production file inode and the snapshot copy inode so that the first intermediate node becomes a descendant of the snapshot copy inode, and splitting the delegated reference count between the relationship of the production file inode and the first intermediate node and the relationship of the snapshot copy inode and the first intermediate node by setting a delegated reference count for the relationship of the snapshot copy inode and the first intermediate node to a value less than the delegated reference count for the relationship of the production file inode and the first intermediate node and decrementing the delegated reference count for the relationship of the production file inode and the first intermediate node by said value;
• the data processor responding to a request from one of the client computers for writing data to the production file at an offset encompassed by the first intermediate node by comparing the delegated reference count for the relationship of the production file inode and the first intermediate node to the reference count for the first intermediate node, and upon finding that the comparison indicates that the first intermediate node is a shared intermediate node, allocating a second intermediate node and decrementing the reference count for the first intermediate node by the delegated reference count for the relationship of the production file inode and the first intermediate node and linking the second intermediate node to the production file inode in place of the first intermediate node so that the second intermediate node becomes a descendant of the production file inode and the first intermediate node is no longer a descendant of the production file inode, and writing the data to the production file at the offset encompassed by the first intermediate node.

A network file server comprising:

• a network adapter for coupling the network file server to a data network of client computers;
• data storage storing files;
• and
• a data processor coupled to the data storage and the network adapter for access of the client computers to the files stored in the data storage;
• the files in the data storage being organized as a hierarchy including inodes and data blocks, the files stored in the data storage including a production file having a first data block in the hierarchy, the first data block being a descendant of the production file inode in the hierarchy, and the data storage storing a reference count for the first data block, and the data storage storing a delegated reference count for the relationship of the production file inode and the first data block;
• the data processor being programmed with a snapshot copy facility, the snapshot copy facility being executable by the data processor to create in the data storage a snapshot copy of the production file by allocating a snapshot copy inode and sharing the first data block between the production file inode and the snapshot copy inode so that the first data block becomes a descendant of the snapshot copy inode, and splitting the delegated reference count between the relationship of the production file inode and the first data block and the relationship of the snapshot copy inode and the first data block;
• and
• the snapshot copy facility being executable by the data processor to respond to a request from one of the client computers for writing data to the production file at an offset encompassed by the first data block by comparing the delegated reference count for the relationship of the production file inode and the first data block to the reference count for the first data block, and upon finding that the comparison indicates that the first data block is a shared block, allocating a second data block, writing to the second data block and decrementing the reference count for the first data block by the delegated reference count for the relationship of the production file inode and the first data block and linking the second data block to the production file inode in place of the first data block so that the second data block becomes a descendant of the production file inode and the first data block is no longer a descendant of the production file inode.