Data set recovery by codeword overlay

A data storage device configurable to read at least one encoded data fragment from a data storage medium, characterized by comprising:

• a means for reading said encoded data fragments from said data storage medium;
• a means for applying at least one decoding algorithm to said encoded data fragments;
• a first memory area configurable to store status data concerning decoding quality metrics of said encoded data fragments;
• and
• a second memory area configurable to store decoded said data fragments;
• said data storage device being arranged to operate to recover data written on said data storage medium as a plurality of encoded data fragments by:
• performing a first read operation to read at least one encoded data fragment of said plurality of encoded data fragments from said data storage medium;
• storing a first status data indicating whether said at least one data fragment has been correctly read;
• if said at least one data fragment is correctly read, writing said at least one read data fragment to said second memory area;
• attempting to decode said at least one encoded data fragment in said second memory area;
• if said attempted decoding is unsuccessful, performing a second read operation for re-reading said at least one encoded data fragment from said data storage medium;
• attempting to decode said re-read encoded data fragment;
• and
• if said re-read data fragment his fewer bytes in error than said at least one encoded data fragment, overwriting said at least one encoded data fragment in said second memory area with said re-read encoded data fragment.

A method of recovering a data set written to a data storage medium as a first plurality of encoded data fragments said method comprising the steps of:

• performing a read operation of said data set to read at least one of said plurality of encoded data fragments comprising said data set;
• storing said read at least one data fragment in an area of a buffer memory reserved for storing data fragments of said data set;
• storing in a memory device a quality metric data of said read operation of said at least one data fragment;
• decoding said data set comprising said plurality of fragments stored within said buffer memory;
• if said step of decoding said data set within said buffer memory fails, performing a re-read operation to re-read incorrectly read data fragments of said data set from said data storage medium;
• and
• if said re-read data fragment has fewer bytes in error than said at least one data fragment, overwriting said at least one data fragment with said re-read data fragment in said buffer memory.

A method of recovering data written onto a data storage medium as a plurality of encoded data fragments, said method comprising the steps of:

• reading from said data storage medium a data set comprising a plurality of codeword pairs;
• checking a header parity data of each said codeword pair;
• for individual said codeword pairs, decoding C1 redundancy encoding data from said codeword pair, and using said C1 redundancy data to correct one or a plurality of incorrectly read said codeword pairs;
• storing in a memory, a first status data indicating a number of corrupted bytes of data corrected by said C1 redundancy coding;
• applying a second redundancy decoding algorithm for decoding C2 redundancy data of a plurality of sub-data sets within said data set;
• using said C2 redundancy encoded data to reconstruct missing or corrupted bytes of data in said data set;
• and
• if said C2 correction fails to fully correct said data set, then re-reading from said data storage medium individual codeword pairs from said data set, said step of re-reading individual codeword pairs comprising:
• (a) reading said status data indicating whether a codeword pair was recovered and indicating a number of bytes in error in said codeword pair;
• and
• (b) if said re-read codeword pair has fewer bytes in error than said same codeword pair originally stored within said memory resulting from said earlier read operation, then overwriting said earlier codeword pair with said re-read codeword pair.

A data storage device configurable to read at least one encoded data fragment from a data storage medium, comprising:

• a reader of said encoded data fragments from said data storage medium;
• a source of at least one decoding algorithm to said encoded data fragments;
• a first memory area configurable to store status data concerning decoding quality metrics of said encoded data fragments;
• and
• a second memory area configurable to store decoded said data fragments;
• said data storage device being arranged to operate to recover data written on said data storage medium as a plurality of encoded data fragments by:
• performing a first read operation to read at least one encoded data fragment of said plurality of encoded data fragments from said data storage medium;
• storing a first status data indicating whether said at least one data fragment has been correctly read;
• if said at least one data fragment is correctly read, writing said at least one read data fragment to said second memory area;
• attempting to decode said at least one encoded data fragment in said second memory area;
• if said attempted decoding is unsuccessful, performing a second read operation for re-reading said at least one encoded data fragment from said data storage medium;
• attempting to decode said re-read encoded data fragment;
• and
• if said re-read data fragment has fewer bytes in error than said at least one encoded data fragment, overwriting said at least one encoded data fragment in said second memory area with said re-read encoded data fragment.