Netapp, Inc.

Dhaval Patel

Edward D McClanahan

Manish Swaminathan

John A Muth

Jeffrey S Kimmel

Srinath Krishnamachari

Chaitanya V Patel

Sriranjani Babu

Mandar Naik

A technique reduces an amount of metadata stored in a memory of a node in a cluster. An extent store layer of a storage input/output (I/O) stack executing on the node stores key-value pairs in a plurality of data structures, e.g., cuckoo hash tables, resident in the memory. The cuckoo hash table embodies metadata that describes an extent and, as such, may be organized to associate a location on disk with a value that identifies the location on disk. The value may be embodied as a locator that includes a reference count used to support deduplication functionality of the extent store layer with respect to the extent. The reference count is divided into two portions: a delta count portion stored in memory for each slot of the hash table and an overflow count portion stored on disk in a header of each extent. One bit of the delta count portion is reserved as an overflow bit that indicates whether the in-memory reference count has overflowed. Another bit of the delta count portion is reserved as a sign bit that indicates whether the value of the remaining delta count portion, which stores the 'delta' of the reference count, is positive or negative. Overflow updates to the overflow count portion on disk are postponed until all of the bits of the delta count portion are consumed as negative/positive transitions.

Technique for reducing metadata stored in a memory of a node

A rate matching technique may be configured to adjust a rate of cleaning of one or more selected segments of the storage array to accommodate a variable rate of incoming workload processed by a storage input/output (I/O) stack executing on one or more nodes of a cluster. An extent store layer of the storage I/O stack may clean a segment in accordance with segment cleaning which, illustratively, may be embodied as a segment cleaning process. The rate matching technique may be implemented as a feedback control mechanism configured to adjust the segment cleaning process based on the incoming workload. Components of the feedback control mechanism may include one or more weight schedulers and various accounting data structures, e.g., counters, configured to track the progress of segment cleaning and free space usage. The counters may also be used to balance the rates of segment cleaning and incoming I/O workload, which may change depending upon an incoming I/O rate. When the incoming I/O rate changes, the rate of segment cleaning may be adjusted accordingly to ensure that rates are substantially balanced.

Rate matching technique for balancing segment cleaning and I/O workload

An optimized segment cleaning technique is configured to efficiently clean one or more selected portions or segments of a storage array coupled to one or more nodes of a cluster. A bottom-up approach of the segment cleaning technique is configured to read all blocks of a segment to be cleaned (i.e., an 'old' segment) to locate extents stored on the SSDs of the old segment and examine extent metadata to determine whether the extents are valid and, if so, relocate the valid extents to a segment being written (i.e., a 'new' segment). A top-down approach of the segment cleaning technique obviates reading of the blocks of the old segment to locate the extents and, instead, examines the extent metadata to determine the valid extents of the old segment. A hybrid approach may extend the top-down approach to include only full stripe read operations needed for relocation and reconstruction of blocks as well as retrieval of valid extents from the stripes, while also avoiding any unnecessary read operations of the bottom-down approach.

Optimized segment cleaning technique

A cluster-wide consistency checker ensures that two file systems of a storage input/output (I/O) stack executing on each node of a cluster are self-consistent as well as consistent with respect to each other. The file systems include a deduplication file system and a host-facing file system that cooperate to provide a layered file system of the storage I/O stack. The deduplication file system is a log-structured file system managed by an extent store layer of the storage I/O stack, whereas the host-facing file system is managed by a volume layer of the stack. Illustratively, each log-structured file system implements a key-value store and cooperates with other nodes of the cluster to provide a cluster-wide (global) key-value store. The consistency checker verifies and/or fixes on-disk structures of the layered file system to ensure its consistency. To that end, the consistency checker may determine whether there are inconsistencies in the key-value store and, if so, reconciles those inconsistencies from a client (volume layer) perspective.

Consistency checker for global de-duplication clustered file system

A technique recovers from a low space condition associated with storage space reserved in an extent store to accommodate write requests received from a host and associated metadata managed by a layered file system of a storage input/output (I/O) stack executing on one or more nodes of a cluster. The write requests, including user data, are persistently recorded on non-volatile random access memory (NVRAM) prior to returning an acknowledgement to the host by a persistence layer of the storage I/O stack. Volume metadata managed by a volume layer of the layered file system is embodied as mappings from logical block addresses (LBAs) of a logical unit (LUN) accessible by the host to extent keys maintained by an extent store layer of the layered file system. Extent store metadata managed by the extent store layer is embodied as mappings from the extent keys to the storage locations of the extents on storage devices of storage arrays coupled to the nodes of the cluster. The space recovery technique accounts for storage space consumed in the extent store by user operations, i.e., write operations for the user data stored on the NVRAM at the persistence layer as well as the associated volume and extent store metadata, to ensure that the user data and associated metadata can be safely and reliably persisted in the extent store even during a low space condition.

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Sunnyvale, CA, United States of America

Dhaval Patel