Log structured array storage subsystem using LSA directory and LSA sub-directory stored in different storage media

A data processing system, comprising:

• a host system;
• a log structured array (LSA) storage subsystem in communication with said host system;
• an LSA directory having a logical track address for all logical tracks in said LSA storage subsystem, said LSA directory being maintained in a first storage medium;
• and,
• an LSA sub-directory comprising a logical track address for each of a predetermined number of most recently accessed logical tracks in said LSA storage subsystem, said LSA sub-directory being maintained in a second storage medium.

In a log structured array (LSA) storage subsystem comprising an array control unit, a storage array of storage devices, an LSA sub-directory in said array control unit, an LSA directory in said storage array, a write buffer, and a valid in track segment bit map, a method of writing data, comprising the steps of:

• (a) determining whether there is sufficient space in write buffer to store data A;
• (b) writing said data A into write buffer if there is sufficient space in said write buffer;
• (c) determining whether an address corresponding to said data A is maintained in either said LSA sub-directory or said LSA directory;
• and
• (d) if said address is found, determining the segment where the previous version of said data A is stored and turning off the bit in said valid tracks in segment bit map corresponding to the previous version of said data A, thereby indicating that the previous version of said data is no longer valid.

In a log structured array (LSA) storage subsystem comprising an array control unit, a storage array of storage devices, an LSA sub-directory in said array control unit, an LSA directory in said storage array, a write buffer, and a valid in track segment bit map, a method of garbage collection, comprising the steps of:

• (a) selecting a segment having a segment directory in said storage array for garbage collection according to a predetermined criterion;
• (b) finding, using said segment directory, the physical address of each track in said segment having its bit set to on in said valid tracks in segment bit map;
• (c) reading each of said tracks in said segment into said write buffer;
• and,
• (d) writing the content of said write buffer into a free segment of storage array.