System for managing log structured array (LSA) of DASDS by managing segment space availability and reclaiming regions of segments using garbage collection procedure

摘要

Seek affinity is preserved in a segment oriented, cached, log structured array (LSA) of DASDs responsive to accesses dominated by sequential read and random writes of logical tracks stored in the segments. This is achieved by collecting all the write modified read active tracks and clean read active tracks either destaged from the cache or garbage collected from the LSA and rewriting them out to the LSA as segments into regions of contiguous segments of read active tracks. Also, all write modified read inactive tracks and clean read inactive tracks either destaged from cache or garbage collected from the LSA are collected and rewritten out to the LSA as segments into regions of contiguous segments of read inactive tracks. Garbage collection is initiated when the detected free space in a region falls below a threshold and continues until the collected segments exceed a second threshold. Alternatively, write age of logical tracks may be used instead of read activity so as to cluster LSA DASDs into a region of segments formed from old write active logical tracks and a region of current write active logical tracks.