Abstract: A technique provides preferential treatment to metadata over user data when protecting data in a mapped-RAID system. The technique involves generating metadata based on user data, storing the metadata in mirrored storage of the mapped-RAID system (e.g., 2-way mirrored storage), and storing the user data in non-mirrored storage of the mapped-RAID system (e.g., writing user data with parity in accordance with RAID 6). The mapped-RAID system provides reliability preference toward maintaining the metadata over maintaining the user data while the metadata and the user data are stored within the mapped-RAID system. Accordingly, the technique is able to concurrently provide high reliability and high storage efficiency.

Abstract: Techniques for rebuilding space accounting counters in mapping layers of storage appliances. The techniques include uniquely associating top levels of a mapping layer of a storage appliance with respective storage objects. The techniques further include determining amounts of logical storage space consumed by the respective storage objects from mappings of LBAs of the respective storage objects to virtual blocks of a virtual layer of the storage appliance. The techniques further include determining amounts of physical storage space consumed by the respective storage objects from logged information pertaining to each leaf pointer of a leaf level of the mapping layer that points to a virtual block in the virtual layer, each virtual block being mapped to a physical block in a physical layer of the storage appliance. The techniques further include using multi-threading to determine amounts of logical storage space consumed by dynamically adjustable ranges of the respective storage objects.

Abstract: A method of operating a storage appliance is provided.

Abstract: A technique of protecting data in a data storage system includes, in response to receiving a write request that specifies data to be written in the data storage system, calculating an error detection code (EDC) of the specified data. The technique further includes persisting the specified data and the EDC in persistent cache and, in response to receiving a read request for reading the specified data, validating the specified data using the EDC before returning the specified data in satisfaction of the read request.

Abstract: Techniques for providing effective utilization of different drive capacities in storage appliances. The techniques include providing a storage drive array that has a first set of storage drives and a second set of storage drives. Each storage drive in the first set has a first drive capacity and each storage drive in the second set has a second drive capacity. The first drive capacity is higher than the second drive capacity. The techniques include allocating, within the first drive capacity, at least a first sub-capacity and a second sub-capacity. The first sub-capacity is equal to the second drive capacity. The techniques include placing blocks of hot data in the first sub-capacities of the storage drives in the first set and/or the second drive capacities of the storage drives in the second set, and placing blocks of cold data in the second sub-capacities of the storage drives in the first set.

Abstract: Technology for configuration metadata recovery that detects a reliability failure regarding configuration metadata stored in non-volatile data storage of a data storage system. The configuration metadata indicates how a metadata database is stored in the non-volatile data storage of the data storage system. In response to detection of the reliability failure regarding the configuration metadata, the technology identifies valid generations of the configuration metadata that are currently stored in the non-volatile data storage of the data storage system, and determines a user-selected one of the valid generations of the configuration metadata. The metadata database is accessed based on the user-selected one of the valid generations of the configuration metadata.

Abstract: A technique for managing data storage includes generating entropy of blocks on a per-block basis and selectively performing inline compression on blocks based at least in part on their entropy. Entropy of a block provides a rough measure of the block's compressibility. Thus, using per-block entropy enables a storage system to steer compression decisions, e.g., whether to compress and/or how much to compress, flexibly and with high granularity, striking a balance between throughput and storage efficiency.

Abstract: A method is used in ensuring data integrity in data storage. A set of physical pages that include data for a virtual page is identified on a storage device. A set of reconstructed pages is generated from other storage devices, and each reconstructed page corresponds to a page in the set of physical pages. One or more pages from the set of physical pages and the set of reconstructed pages with data yielding a checksum that matches a checksum for the virtual page is identified, and data corresponding to the virtual page from the identified one or more pages is obtained.

Abstract: A method performed by a computing device having memory is provided. The method includes (a) detecting corruption in a first page description block (PDB) of a plurality of PDBs stored in sequence in the memory, each PDB storing a set of page descriptors (PDs) that point to pages of data sequentially stored in the memory that are part of a single transaction, PDBs that represent the same transaction being contiguous within the sequence; (b) searching for a second PDB of the plurality of PDBs, the second PDB satisfying the following criteria: (1) it is not corrupted, and (2) it represents a same transaction as the first PDB; and (c) reconstructing the first PDB using the second PDB. An apparatus, system, and computer program product for performing a similar method are also provided.

Abstract: A method, computer program product, and computer system for identifying a bit for an allocation unit. It may be determined if data has been modified on the allocation unit while degraded. A rebuild of the allocation unit may be executed when the bit is a first value. The rebuild of the allocation unit may be skipped when the bit is a second value.

Abstract: A method of managing CPU cores in a data storage apparatus (DSA) configured to perform both host I/O (Input/Output) processing and background storage processing is provided. The method includes (a) selectively classifying background storage tasks in one of a first classification for longer-running tasks and a second classification for shorter-running tasks; (b) selecting CPU cores that are running fewer than a threshold number of first-classification background tasks to process host I/O requests; and (c) processing the host I/O requests on their selected CPU cores. An apparatus, system, and computer program product for performing a similar method are also provided.

Abstract: A technique of protecting data in a data storage system includes, in response to receiving a write request that specifies data to be written in the data storage system, calculating an error detection code (EDC) of the specified data. The technique further includes persisting the specified data and the EDC in persistent cache and, in response to receiving a read request for reading the specified data, validating the specified data using the EDC before returning the specified data in satisfaction of the read request.

Abstract: A method of validating metadata pages that map to user data in a data storage system is provided. The method includes (a) obtaining first information stored for a first metadata page and second information stored for a second metadata page, the first and second metadata pages having a relationship to each other within a hierarchy of metadata pages for accessing user data; (b) performing a consistency check between the first information and the second information, the consistency check producing a first result in response to the relationship being verified and a second result otherwise; and (c) in response to the consistency check yielding the second result, performing a corrective action to restore consistency between the first and second information. An apparatus, system, and computer program product for performing a similar method are also provided.

Abstract: A method of managing operation of a data storage system (DSS) is provided. The method includes (a) reserving space within a dedicated metadata storage region (DMSR); (b) in response to determining that accommodating a storage request requires use of the reserved space, entering a restricted write mode; (c) while operating in the restricted write mode, using the reserved space in a process that frees space within the DMSR outside the reserved space; and (d) exiting the restricted mode in response to freeing space within the DMSR outside the reserved space. An apparatus, system, and computer program product for performing a similar method are also provided.

Abstract: Host data stored in one or more source physical extents of non-volatile data storage is identified as valid and determined to be infrequently written by host I/O requests, and is therefore compressed to generate a highly compressed version of the valid host data. The highly compressed version is then stored into at least one target physical extent. The valid host data may be initially compressed before it is stored in the source physical extent(s), and may be re-compressed to generate the highly compressed version. If the valid host data is also infrequently read, it may be recompressed using larger blocks of host data than were used to perform the initial compression. The performance tier of the target physical extent may be different from (e.g. lower than) the performance tier of the source physical extent. The technology may be embodied in a background process such as a garbage collector.

Abstract: Coordinating a reclaiming of data storage space among processing nodes of a data storage system includes, by a first node in response to an event, performing local cleanup of first-node mapping data and issuing a request message to a second node, the request message identifying the data storage space to be reclaimed. The event may be a notification from a RAID component rebuilding a RAID volume. In response to the request message, the second node performs local cleanup of second-node mapping data and issues a completion message to the first node indicating that the second node has completed its part of the reclaiming of the data storage space. The first node responds to the completion message by marking the data storage space as being reclaimed and signaling to a source of the event that the data storage space is available for new use.

Abstract: An allocation history is maintained for each node in a multi-node data storage system. The allocation history for each node indicates sets of physical blocks previously allocated to the node to store dirty pages of user data flushed from a cache of the node. The allocation history indicates non-quarantined sets of physical blocks that are currently being used to provide non-volatile data storage to cache flush operations, and quarantined sets of physical blocks not currently being used to provide non-volatile data storage to cache flush operations. Allocation is prevented to any node of any set of physical blocks that is indicated as non-quarantined by any of the allocation histories, and of any set of physical blocks that is indicated as quarantined by any of the allocation histories.

Abstract: A data storage system performs updating of a set of global counters stored in persistent storage accessible to a plurality of processing nodes of a data storage system, the global counters storing respective global count values describing associated units of data storage shared by the processing nodes for performing data storage operations. The updating includes, by each processing node, using a respective set of in-memory delta counters storing respective delta count values to track changes to respective global count values due to data storage operations performed by the processing node with respect to the units of data storage. A summarization process is regularly executed to merge the delta count values of the delta counters of all processing nodes into the respective global counters.

Abstract: An apparatus comprises at least one processing device comprising a processor coupled to a memory; the at least one processing device being configured to: obtain a set of rebuild rate parameters for a given storage device from a storage array comprising a plurality of storage devices; and dynamically regulate a rebuild rate associated with a rebuild process for the given storage device based on the set of rebuild rate parameters obtained from the storage array for the given storage device. For example, the set of rebuild rate parameters include a rebuild capacity parameter and a rebuild time parameter.

Abstract: A method of correcting errors in a data storage system including a first node, a second node, and shared persistent storage (the first and second nodes being configured to process data storage requests) is provided. The method includes (a) reading cached pages from a first cache disposed within the first node, the cached pages being cached versions of respective persistent pages stored in the shared persistent storage; (b) in response to determining that one of the cached pages is corrupted, requesting that the second node return to the first node a corresponding remote page from a second cache disposed within the second node, the cached page and the remote page each caching a same persistent page of the shared persistent storage; and (c) in response to determining that the remote page received from the second node by the first node is not corrupted, correcting the cached page using the remote page.