Adaptive read recovery for NAND flash memory devices

A method of reading data read from a NAND Flash memory device, the method comprising:

• decoding a set of data read from the NAND Flash memory device, using an initial set of hard bit thresholds;
• when the decoding is unsuccessful, performing a read-retry operation that retries the decoding using, in order, each of a plurality of entries in a read-retry table of hard bit thresholds, stopping when decoding based on one of the entries is successful;
• when the read-retry operation is unsuccessful, performing a deep retry operation using a set of log-likelihood ratios (LLRs) that vary in at least one of (a) values, and (b) symmetries, the deep retry operation comprising:
• selecting a first operation for providing the set of LLRs that vary,
• performing the first operation and determining decoder statistics based on the first operation,
• in response to determining that the decoding performance is improving based on a change of the decoder statistics, continuing to use the first operation, and
• in response to the decoding performance not improving, selecting and performing a second operation for providing the set of LLRs that vary;
• and
• communicating the decoded data to a host.