US Patent 9372751 Free space collection in log structured storage systems

A mechanism is provided for optimizing free space collection in a storage system having a plurality of segments. A collection score value is calculated for least one of the plurality of segments. The collection score value is calculated by determining a sum, across tracks in the segment, of the amount of time over a predetermined period of time during which the track has been invalid due to a more recent copy being written in a different segment. Segments are chosen for free space collection based on the determined collection score value.