Selective hard and soft rewrites

A method for reducing rewrite overhead in a sequential access storage system, the method comprising:

• writing a data set to a sequential access medium using a magnetic head, wherein the data set comprises a plurality of encoded data blocks;
• classifying each of the plurality of encoded data blocks on the sequential access medium into one of at least three classes of write quality, wherein the at least three classes of write quality include:
• a hard rewrite class for which rewrites are necessary to prevent data loss, wherein the encoded data blocks will be classified in the hard rewrite class conditioned upon whether a number of run length limited decoding errors is greater than a first predetermined threshold;
• and either:
• a number of byte errors is greater than a second predetermined threshold;
• or
• an uncorrectable error is detected;
• a soft rewrite class for which rewrites are desirable but not necessary;
• and
• a no rewrite class for which no rewrite is needed or desired;
• and
• selectively rewriting the encoded data blocks in a rewrite area of the sequential access medium based at least in part on the write quality class.

A computer program product, the computer program product comprising a computer readable storage medium having program instructions embodied therewith, the program instructions executable by an apparatus to cause the apparatus to:

• write a data set to a sequential access medium using a magnetic head, wherein the data set comprises a plurality of encoded data blocks;
• classify each of the plurality of encoded data blocks on the sequential access medium into one of at least three classes of write quality, wherein the at least three classes of write quality comprise:
• a hard rewrite class for which rewrites are necessary to prevent data loss, wherein the encoded data blocks will be classified in the hard rewrite class conditioned upon whether a number of run length limited decoding errors is greater than a first predetermined threshold;
• and either:
• a number of byte errors is greater than a second predetermined threshold;
• or
• an uncorrectable error is detected;
• a soft rewrite class for which rewrites are desirable but not necessary;
• and
• a no rewrite class for which no rewrite is needed or desired;
• and
• selectively rewrite the encoded data blocks in a rewrite area of the sequential access medium based at least in part on the write quality class.

An apparatus, comprising:

• a controller;
• and
• logic integrated with the controller, executable by the controller, or integrated with and executable by the controller, the logic being configured to:
• write a data set to a sequential access medium using a magnetic head, wherein the data set comprises a plurality of encoded data blocks;
• classify each of the plurality of encoded data blocks on the sequential access medium into one of at least three classes of write quality, wherein the at least three classes of write quality comprise:
• a hard rewrite class for which rewrites are necessary to prevent data loss, wherein the encoded data blocks will be classified in the hard rewrite class conditioned upon whether a number of run length limited decoding errors is greater than a first predetermined threshold;
• and either:
• a number of byte errors is greater than a second predetermined threshold;
• or
• an uncorrectable error is detected;
• a soft rewrite class for which rewrites are desirable but not necessary;
• and
• a no rewrite class for which no rewrite is needed or desired;
• and
• selectively rewrite the encoded data blocks in a rewrite area of the sequential access medium based at least in part on the write quality class.