Abstract: A technique efficiently determines accurate storage space savings reported to a host coupled to a reference-counted storage system that employs de-duplication and compression, wherein the storage space savings relate to snapshots and/or clones supported by the storage system. The snapshot/clone may be represented as an independent volume, and embodied as a respective read-only copy (snapshot) or read-write copy (clone) of a parent volume. Metadata is illustratively organized as one or more multi-level dense trees, wherein each level of each dense tree includes volume metadata entries for storing the metadata. The metadata is illustratively embodied as mappings from LBAs of a LUN to extent keys. Space adjustment counters, such as clone space adjustment (CSA) and diverged space adjustment (DSA) counters, may be employed when determining the storage space savings. The CSA counter is equal to the sum of mapped storage space across all levels of a dense tree.

Abstract: A consistency checker is configured to perform repairs to one or more multi-level dense tree metadata structures shared between volumes managed by a volume layer of a storage input/output (I/O) stack executing on one or more nodes of a cluster. The volumes include a parent volume and a snapshot and/or clone, wherein the snapshot/clone may be represented as an independent volume, and embodied as a respective read-only copy (snapshot) or read-write copy (clone) of the parent volume. Illustratively, the consistency checker verifies and/or fixes (i.e., repairs) on-disk structures of the volume layer, e.g., the shared dense tree, according to a distributed repair procedure that maintains consistency properties across all volumes in a volume family and avoid cyclic repairs made in the context of different volumes sharing the dense tree.

Abstract: A technique efficiently manages a snapshot and/or clone by a volume layer of a storage input/output (I/O) stack executing on one or more nodes of the cluster. According to the technique, an ownership attribute is included in metadata entries of a dense tree data structure for extents that eliminates otherwise needed reference count operations for the snapshots and reduces reference count operations for the clones. Illustratively, a copy of a parent dense tree level created by a copy-on-write (COW) operation is referred to as a “derived level”, whereas the existing level of the parent dense tree is referred to as a “source level”. The source level may be persistently linked to the derived level by keeping “level identifying key information” in a respective dense tree source level header. Moreover, two different types of dense tree derivations are defined: a derive relationship and a reverse-derive relationship.

Abstract: A technique efficiently determines accurate storage space savings reported to a host coupled to a reference-counted storage system that employs de-duplication and compression, wherein the storage space savings relate to snapshots and/or clones supported by the storage system. The snapshot/clone may be represented as an independent volume, and embodied as a respective read-only copy (snapshot) or read-write copy (clone) of a parent volume. Metadata is illustratively organized as one or more multi-level dense trees, wherein each level of each dense tree includes volume metadata entries for storing the metadata. The metadata is illustratively embodied as mappings from LBAs of a LUN to extent keys. Space adjustment counters, such as clone space adjustment (CSA) and diverged space adjustment (DSA) counters, may be employed when determining the storage space savings. The CSA counter is equal to the sum of mapped storage space across all levels of a dense tree.

Abstract: A consistency checker is configured to perform repairs to one or more multi-level dense tree metadata structures shared between volumes managed by a volume layer of a storage input/output (I/O) stack executing on one or more nodes of a cluster. The volumes include a parent volume and a snapshot and/or clone, wherein the snapshot/clone may be represented as an independent volume, and embodied as a respective read-only copy (snapshot) or read-write copy (clone) of the parent volume. Illustratively, the consistency checker verifies and/or fixes (i.e., repairs) on-disk structures of the volume layer, e.g., the shared dense tree, according to a distributed repair procedure that maintains consistency properties across all volumes in a volume family and avoid cyclic repairs made in the context of different volumes sharing the dense tree.

Abstract: A recovery consumer framework provides for execution of recovery actions by one or more recovery consumers to enable efficient recovery of information (e.g., data and metadata) in a storage system after a failure event (e.g., a power failure). The recovery consumer framework permits concurrent execution of recovery actions so as to reduce recovery time (i.e., duration) for the storage system. The recovery consumer framework may coordinate (e.g., notify) the recovery consumers to serialize execution of the recovery actions by those recovery consumers having a dependency while allowing concurrent execution between recovery consumers having no dependency relationship. Each recovery consumer may register with the framework to associate a dependency on one or more of the other recovery consumers. The dependency association may be represented as a directed graph where each vertex of the graph represents a recovery consumer and each directed edge of the graph represents a dependency. The framework may traverse (i.e.

Abstract: A recovery consumer framework provides for execution of recovery actions by one or more recovery consumers to enable efficient recovery of information (e.g., data and metadata) in a storage system after a failure event (e.g., a power failure). The recovery consumer framework permits concurrent execution of recovery actions so as to reduce recovery time (i.e., duration) for the storage system. The recovery consumer framework may coordinate (e.g., notify) the recovery consumers to serialize execution of the recovery actions by those recovery consumers having a dependency while allowing concurrent execution between recovery consumers having no dependency relationship. Each recovery consumer may register with the framework to associate a dependency on one or more of the other recovery consumers. The dependency association may be represented as a directed graph where each vertex of the graph represents a recovery consumer and each directed edge of the graph represents a dependency. The framework may traverse (i.e.