Abstract: In one embodiment, a node coupled to one or more storage devices executes a storage input/output (I/O) stack having a volume layer. The volume layer manages volume metadata embodied as mappings from offsets of a logical unit (LUN) to extent keys associated with storage locations for extents on the one or more storage devices. Volume metadata is maintained as a dense tree metadata structure representing successive points in time. The dense tree metadata structure has multiple levels, wherein a top level of the dense tree metadata structure represents newer volume metadata changes and descending levels of the dense tree metadata structure represent older volume metadata changes. The node accesses a latest version of changes to the volume metadata by searching from the top level to the descending levels in the dense tree metadata structure.

Abstract: The embodiments described herein are directed to an organization of metadata managed by a volume layer of a storage input/output (I/O) stack executing on one or more nodes of a cluster. The metadata managed by the volume layer, i.e., the volume metadata, is illustratively embodied as mappings from addresses, i.e., logical block addresses (LBAs), of a logical unit (LUN) accessible by a host to durable extent keys maintained by an extent store layer of the storage I/O stack. In an embodiment, the volume layer organizes the volume metadata as a mapping data structure, i.e., a dense tree metadata structure, which represents successive points in time to enable efficient access to the metadata.

Abstract: In one embodiment, a parallel (e.g., tiered) logging technique is provided to deliver low latency acknowledgements of input/output (I/O) requests, such as write requests, while avoiding loss of data. Write data may be stored (copied) as a log in a portion of a dynamic random access memory and a non-volatile random access memory (NVRAM). The NVRAM may be configured as, e.g., a persistent write-back cache of the node, while parameters of the request may be stored in another portion of the NVRAM configured as the log (NVLog). The write data may be organized into separate variable length blocks or extents and “written back” out-of-order from the write-back cache to storage devices, such as SSDs, e.g., organized into a data container (intended destination of the write request). The write data may be preserved in the NVlog until each extent is safely stored on SSD.