Emc IP Holding Company LLC

Emc Corporation

Soumyadeep Sen

Alexander S Mathews

Rohit K Chawla

Dixitkumar Vishnubhai Patel

Kumari Bijayalaxmi Nanda

Philippe Armangau

Christopher Alan Seibel

Ahsan Rashid

Marc A De Souter

Morgan A Clark

Michal Marko

Walter Forrester

Sitaram D Pawar

Yubing Wang

Bijayalaxmi Nanda

The technology described herein efficiently determines whether a real inode is shared among views, or owned. In-memory data structures include a view snapshot generation counter that is increased as a snapshot that generates a view is created, and an inode total weight. An in-memory virtual inode cache dataset for a filesystem object associated with the view is instantiated with the value of snapshot generation counter, sharing-related data based on the inode mapping file entry for the object, and an inode access weight. To determine whether the inode is shared (and needs to be split), such as on a write to the object, the in-memory data is evaluated. The real inode is shared if the generation counters are unequal, if the sharing-related data indicates sharing at an intermediate indirect block level, or indicates sharing at the inode level and the inode access weight is less than the inode total weight.

Determining a sharing relationship of a file in namespace snapshots

Described is hard link handling when a directory snapshot exists that includes the hard link's connected file object. A hard link is created by allocating a virtual inode number for the hard link, with the virtual inode number mapped to a real inode number that identifies a real inode of the file object; the hard link is assigned weight. A total weight associated with the real inode is increased by the hard link weight, and a hard link data store is updated with an entry for the hard link. Upon receiving data write request to the hard link, weight data determines that the file object is shared as a result of the snapshot; the hard link is disassociated from the real inode file, and associated with a new real inode number and new real inode of a new file object. The data is written based on the new real inode.

Hard link handling with directory snapshots

A method, computer program product, and computer system for maintaining a back pointer from a physical layer block (PLB) to a virtual layer block (VLB) in a multi-level hierarchical file system. A generation number may be maintained in the VLB, wherein the generation number may indicate when data is moved from the PLB to another PLB. An object may be reconstructed in the multi-level hierarchical file system based upon, at least in part, at least one of the back pointer and the generation number.

System and method for inline recovery of a file system resource allocator

Technology described herein can perform deletion of a snapshot or portion thereof. In an embodiment, a system can comprise a processor and a memory that stores executable instructions that, when executed by the processor, facilitate performance of operations. The operations can comprise, to delete a snapshot, or a portion of a snapshot, of a real filesystem, reading an inode mapping file (IMF) of the snapshot that indexes a virtual inode number (VIN) corresponding to a real inode. The operations further can comprise identifying the real inode of the snapshot referenced by the VIN, identifying a file object corresponding to the real inode, and deleting the file object from the snapshot.

Deletion of snapshot of filesystem

An apparatus includes a processing device configured to generate log records each representing a pointer from a leaf page in a logical address space of a storage system to a virtual block address and comprising a leaf page address of the leaf page. The processing device is also configured to identifying a subset of the log records representing pointers to a given virtual block address to determine a first reference count, and to determine whether the first reference count is different than a second reference count obtained from a given virtual entry of a given virtual block structure that corresponds to the given virtual block address. The processing device is further configured, responsive to determining that the first and second reference counts are different, to modify pointers to the given virtual block address in leaf pages with associated leaf page addresses in the identified subset of the log records.

Mapping virtual block addresses to portions of a logical address space that point to the virtual block addresses

Techniques for performing space accounting for volume families. The techniques include maintaining two counters for each volume family, including a first counter that tracks a first amount of physical space allocated to volumes in the volume family based on the number of pages written to the volumes, and a second counter that tracks a second amount of physical space owned by the volume family, and maintaining a third counter for each volume in each branch of the volume family that tracks a number of pages among a total number of pages written to the volume that were overwritten in the immediate sequential next volume in the same branch as the volume. By maintaining, for each volume family, the first counter and the second counter, and, for each volume in the volume family, the third counter, space accounting metrics can be obtained that allow data storage activities to be performed efficiently.

Mechanisms for performing accurate space accounting for volume families

A method of repairing an indirect addressing structure of a file system damaged by corruption of a virtual data block (VDB) mapping data stored in corresponding physical data blocks (PDBs) includes scanning PDB descriptors to identify PDBs storing data mapped by the corrupted VDB, where each identified PDB includes a set of PDB entries each having a backward pointer identifying a corresponding VDB entry of a corresponding VDB. The identified PDBs are scanned to identify PDB entries whose backward pointers refer to VDB entries of the corrupted VDB, then a replacement VDB is created by (1) for each of the identified PDB entries, recreating a corresponding VDB entry including a forward pointer to the identified PDB entry, and (2) incorporating the recreated VDB entries into the replacement VDB. The replacement VDB is then incorporated into the indirect addressing structure in place of the corrupted VDB.

Data storage system with repair of virtual data blocks of internal file system

A technique for repairing an indirect addressing structure of a file system damaged by corruption of a mid-level mapping (MID) page includes scanning selected leaf pages to identify leaf pages associated with the corrupted MID page, then recreating the MID page by recreating pointers to the identified leaf pages. The scanning includes (1) based on an association of groups of leaf pages with corresponding sets of families of storage objects, scanning the leaf pages of only those groups of leaf pages associated with the family of storage objects for the corrupted MID page. The scanning further includes (2) performing a two-pass process including first identifying all leaf pages for the logical offset range of the corrupted MID page and then pruning those identified leaf pages that are reachable via non-corrupted MID pages, yielding the leaf pages for the corrupted MID page only, usable to recreate the corrupted MID page.

Data storage system with repair of mid-level mapping blocks of internal file system

Techniques for tracking pages that are unshared among snapshot volumes and their parent volume in a volume family. The techniques include maintaining a first counter that tracks a first number ('SnapOwnedCount') of pages among a total number of pages written to a volume that were overwritten in the immediate sequential next volume in the same branch as the volume, and a second counter that tracks a second number ('UnsharedWithParentCount') of pages among the total number of pages written to the volume that were overwritten in any sequential next volume in the same branch as the volume. By maintaining, for each volume in a volume family, a first counter and a second counter for tracking the SnapOwnedCount and the UnsharedWithParentCount, respectively, data storage recovery can be performed more effectively, allowing selected volumes and/or portions thereof to be deleted while maintaining accurate space accounting information.

Efficient space accounting mechanisms for tracking unshared pages between a snapshot volume and its parent volume

Techniques for processing unaligned IO requests in data storage systems that provide optimization of inline compression. The disclosed techniques employ an unaligned IO cache, which is used by a data storage system to process unaligned IO requests containing data with sizes that are not multiples of a predetermined block size. By employing the unaligned IO cache while processing such unaligned IO requests, the data storage system can reduce the number of read-modify-write sequences required to process a sequential load of unaligned IO requests, thereby reducing the burden on processing resources of the data storage system.

Unaligned IO cache for inline compression optimization

A file server has an extent cache of pointers to leaf-level indirect blocks containing file mapping metadata. The extent cache improves file access read and write performance by returning a mapping for the data blocks to be read or written without having to iterate through intermediate level indirect blocks of the file. In addition, the extent cache contains pointers to the leaf-level indirect blocks in the file system cache. Therefore, in most cases, the time spent looking up pointers in the extent cache is offset by a reduction in the time that would otherwise be spent in locating the leaf-level indirect blocks in the file system cache. In a preferred implementation, the extent cache has a first least recently used (LRU) list and cache entry allocation for production files, and a second LRU list and cache entry allocation for snapshot copies of the production files.

Growing community of inventors

Highland Park, NJ, United States of America

Soumyadeep Sen