Abstract: A method, system, and computer program product for creating and implementing file clones using reverse ditto references. A clone inode is created as a copy of an original inode. The clone inode and the original inode are indistinguishable to an end user. Each additional file clone created spawns a clone inode. An immutable clone-parent inode is created that contains the disk block addresses, while writable clones inode instead contain dittos linking the clone inode to data blocks referenced in the clone-parent inode. Data block address links in the original inode are moved to the new clone-parent inode and dittos replace the original data block address links in the original inode. When a clone file is updated, the new data is written to a new disk location and a corresponding ditto in the clone inode is replaced with a data block link address, keeping the data of the clone-parent inode intact.

Abstract: A computer system having a shared disk file system running on on multiple computers each having their own instance of an operating system and being coupled for parallel data sharing access to files residing on network attached shared disks. Method are provided for use as a parallel file system in a shared disk environment by use of scalable directory service for the system with a stable cursor, a segmented allocation map. Dynamic prefetch and cached balance pools for multiple accesses improve the system. Extended file attributes are used for implementation of Access Control Lists in a parallel file system. Improvements to caching and cache performance developments balance pools for multiple accesses. A metadata node manages file metadata for parallel read and write actions.

Abstract: A computer system having a shared parallel disk file system running on a network for multiple computers each having their own instance of an operating system and with a protocol that makes disks appear to be locally attached to each file system. This parallel file system in a shared disk environment uses scalable directory service method improvements to caching and cache performance developments balance pools for multiple accesses. A metadata node manages file metadata, and locking techniques reduce the overhead of a token manager which is also used in the file system recovery if a computer participating in the management of shared disks becomes unavailable or failed. Synchronous and asynchronous takeover of a metadata node occurs for correction of metadata which was under modification and a new computer node to be a metadata node for that file. Locks are not constantly required to allocate new blocks on behalf of a user.