Abstract: The present invention relates to a system for restoring a file from a snapshot, where a version of the file exists in both an active file system and the snapshot. A twin inode is created in the active file system and comparisons are made between block pointers of the twin inode and the snapshot. If there is a match, the block pointer of the twin inode is moved to the active file system. If there is not a match, a determination is made whether the snapshot block pointer exists in the active file system. If the snapshot block pointer does not exist in the active file system, it is copied to the active file system. If it does exist, then the actual data block pointed to by the snapshot block pointer is copied to the active file system. In this way, a file may be restored without the need to always copy every individual data block or inode from the snapshot.

Abstract: A storage server provides a set of client devices with access to a set of mass storage devices. The storage server receives requests from the client devices, each request representing a storage operation to be performed by the storage server on the set of mass storage devices. The storage server maintains a log of write requests received from the client devices, the log including a separate log entry for each of the write requests, and a separate checksum in each of the log entries. Each checksum is for use by a checksum algorithm in determining data integrity of the corresponding log entry. The checksum algorithm is selected, from among a number of selectable a checksum algorithms, based on one or more predetermined criteria, such as a desired balance between performance and checksum strength.

Abstract: A method and system for reliably performing extra-long operations in a reliable state-full system (such as a file system). The file system includes a separate portion of the file system reserved for files having extra-long operations in progress, including file deletion and file truncation. This separate portion of the file system is called the zombie file space; it includes a separate name space from the regular (“live”) file system that is accessible to users, and is maintained as part of the file system when recording a consistency point.

Abstract: The invention provides a method and system for reducing RAID parity computation following a RAID subsystem failure. Ranges of RAID stripes are assigned to bits in a bitmap that is stored on disk. When writes to the RAID are in progress, the bit associated with the range of stripes in the bitmap is set. When a failure occurs during the write process, the bitmap is analyzed on reboot to determine which ranges of stripes where in the process of being written, and the parity data for only those ranges of stripes is recomputed. Efficiency is increased by use of an in-memory write counter that tracks multiple writes to each stripe range. Using the write counter, the bitmap is written to disk only after each cycle of its associated bitmap bit being set to a value of 1 and then returning to zero. The invention may be installed, modified, and removed at will from a RAID array, and this may be accomplished while the system is in operation.

Abstract: A method and system for reliably performing extra-long operations in a reliable state-full system (such as a file system). The file system includes a separate portion of the file system reserved for files having extra-long operations in progress, including file deletion and file truncation. This separate portion of the file system is called the zombie file space; it includes a separate name space from the regular (“live”) file system that is accessible to users, and is maintained as part of the file system when recording a consistency point.

Abstract: A technique provides on-disk representations of multiple named data streams for a file system of a network storage appliance. The network storage appliance or filer includes a file system that implements a Write Anywhere File Layout (WAFL) disk format, wherein files are described by inodes of which there may be various types, including directory and regular modes. A named stream mode type is defined that represents named data streams in the WAFL file system. Multiple data streams may be stored on disk(s) of the filer as representations embodying the named stream inode type associated with a file. The names and file handles of the data streams are stored in a “hidden” directory within the file system that is referenced by the base inode. The hidden directory is represented as a stream_dir inode type.

Abstract: A technique provides on-disk representations of multiple named data streams for a file system of a network storage appliance. The network storage appliance or filer includes a file system that implements a Write Anywhere File Layout (WAFL) disk format, wherein files are described by inodes of which there may be various types, including directory and regular inodes. A named stream inode type is defined that represents named data streams in the WAFL file system. Multiple data streams may be stored on disk(s) of the filer as representations embodying the named stream inode type associated with a file. The names and file handles of the data streams are stored in a “hidden” directory within the file system that is referenced by the base mode. The hidden directory is represented as a stream_dir inode type.

Abstract: A system that manages a file system for a file server. A file operation is received that signals a reservation operation for a file having a file size. Preferably, the file system uses a write anywhere file system layout, the file operation that signals the reservation operation is a zero length write request, and the file operation that signals the reservation operation includes a parameter that specifies the file size. A number of blocks needed to be reserved to accommodate the file is computed. Preferably, computing the number of blocks needed to be reserved to accommodate the file includes determining a total number of direct and indirect blocks needed to accommodate the file size, and subtracting a total number of blocks already allocated for the file and a total number of cached unallocated blocks for the file from the total number of direct and indirect blocks needed to accommodate the file size.

Abstract: A file folding technique reduces the number of duplicate data blocks of a file consumed on a storage device of a file server configured to generate a persistent image of its active file system at a point in time. According to the file folding technique, if “old” data blocks of the file are over-written with “new” data and that new data is identical to the data of the persistent file image, the old data blocks are “freed” and the file is directed to refer to the persistent image for its data. The invention reduces disk space consumption in a file server configured to generate persistent images of its active file system and, in particular, reduces overall persistent image disk usage.

Abstract: The present invention provides a system and method for restoring a single file from a snapshot without the need to copy every individual block or inode from the snapshot. A file restore process duplicates the inode of a file within the active file system and performs a reconciliation process between the blocks of the twin inode and the snapshot inode. If the file does not exist within the active file system, a new buffer tree is created that points to the data blocks stored in the snapshot.

Abstract: The invention provides a method and system for reliably performing extra-long operations in a reliable state-full system (such as a file system). The system records consistency points, or otherwise assures reliability, notwithstanding the continuous performance of extra-long operations and the existence of intermediate states for those extra-long operations. Moreover, performance of extra-long operations is both deterministic and atomic with regard to consistency points (or other reliability techniques used by the system). The file system includes a separate portion of the file system reserved for files having extra-long operations in progress, including file deletion and file truncation. This separate portion of the file system is called the zombie filespace; it includes a separate name space from the regular (“live”) file system that is accessible to users, and is maintained as part of the file system when recording a consistency point.