DEFERRED REFERENCE COUNT UPDATE TECHNIQUE FOR LOW OVERHEAD VOLUME METADATA

摘要

A deferred refcount update technique efficiently frees storage space for metadata (associated with data) to be deleted during a merge operation managed by a volume layer of a node. The metadata is illustratively volume metadata embodied as mappings from logical block addresses (LBAs) of a logical unit (LUN) to extent keys maintained by an extent store layer of the node. One or more requests to delete (or overwrite) an LBA range within a LUN may be captured as page keys associated with metadata pages during the merge operation and the storage space associated with those metadata pages may be freed in an out-of-band fashion. The page keys of the metadata pages may be persistently recorded in a reference count (refcount) log to thereby allow the merge operation to complete without resolving deletion of the keys. A batch of page keys may be organized as one or more delete requests and, once the merge completes, the keys may be inserted into the refcount log. Subsequently, a deferred reference count update process may be spawned (instantiated) to walk through the page keys stored in the refcount log and delete each key, e.g., from the extent store layer, independently and out-of-band from the merge operation.

主权项

1. A method comprising:
receiving a write request directed towards a logical unit (LUN), the write request having data, a logical block address (LBA) and a length representing a first address range of the LUN, the write request processed at a storage system having a memory; associating a first data key with the data; storing the first data key in a first data entry of a metadata structure, the first data entry representing the first address range of the LUN; merging the first data entry of the metadata structure with a second data entry of the metadata structure to form a third data entry, the second data entry representing a second address range, the third data entry representing a merge of the first address range and the second address range, the second data entry including a second data key, the second data entry stored in an extent at a location on a storage array of solid state drives (SSDs) attached to the storage system, the extent associated with a metadata key; storing the third data entry on the storage array; inserting the metadata key in a delete log; and processing the delete log to delete the second data entry from the storage array.