Abstract: The disclosure relates in some aspects to a design for a data storage apparatus with a non-volatile memory that includes a block of memory comprising N wordlines partitioned into a first sub-block comprising a first subset of the N wordlines and a second sub-block comprising a second subset of the N wordlines different than the first subset. In some aspects, the disclosure relates to detecting a failure in a first sub-block. The second sub-block is then marked, in response to a failure detection in the first sub-block, with an initial designation as an unusable sub-block, and a test of the second sub-block is performed to determine a usability of the second sub-block. Based on the test, the second sub-block is then marked with a second designation that is one of a tested usable sub-block or a tested unusable sub-block.