Technique for quantifying logical space trapped in an extent store

摘要

A technique quantifies logical storage space trapped in an extent store due to overlapping write requests associated with volume metadata managed by the volume layer. The volume metadata is illustratively organized as a multi-level dense tree metadata structure, wherein each level of the dense tree metadata structure (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 a next lower level of the dense tree in accordance with a merge operation. Illustratively, the technique may be invoked during the merge operation to examine the volume metadata entries at each level of the dense tree involved in the merge and determine the LBA range overlap of the entries. To that end, the technique may include an algorithm configured to calculate the overlapping space per level and then aggregate the overlapping space of all levels involved in the merge operation to arrive at a result that quantifies the logical storage space trapped in the extent store.

主权项

1. A method comprising:
receiving first and second write requests directed towards a logical unit (LUN), the first and second write requests having respective first and second data, the first and second write requests representing respective first and second offset ranges of the LUN, the second offset range overlapping a portion of the first offset range, the write requests processed at a storage system having a memory; associating first and second keys with the respective first and second data; storing the first and second keys in respective first and second data entries of a metadata structure, the first data entry having a first offset and a first original length representing the first offset range of the LUN, the second data entry having a second offset and a second original length representing the second offset range of the LUN, wherein the first data entry includes a first length decreased from the first original length by an amount of overlap of the second offset range with the first offset range; subtracting the first length from the first original length, thereby calculating an amount of trapped logical space associated with the first data entry; and storing the first and second data in a storage array attached to the storage system.