Reconstruction of dense tree volume metadata state across crash recovery

摘要

Embodiments herein are directed to efficient crash recovery of persistent metadata managed by a volume layer of a storage input/output (I/O) stack executing on one or more nodes of a cluster. Volume metadata managed by the volume layer is organized as a multi-level dense tree, wherein each level of the dense tree includes volume metadata entries for storing the volume metadata. When a level of the dense tree is full, the volume metadata entries of the level are merged with the next lower level of the dense tree. During a merge operation, two sets of generation IDs may be used in accordance with a double buffer arrangement: a first generation ID for the append buffer that is full (i.e., a merge staging buffer) and a second, incremented generation ID for the append buffer that accepts new volume metadata entries. Upon completion of the merge operation, the lower level (e.g., level 1) to which the merge is directed is assigned the generation ID of the merge staging buffer.