Read retry with physical defect judgement

A method for operating NAND memory, the method comprising:

• determining that a read error has occurred when reading a page of NAND memory cells connected to a word line in a block at a first set of read reference levels;
• determining a second set of read reference levels that are able to successfully read the page of NAND memory cells in response to the read error at the first set of read reference levels;
• and
• determining that the read error is due to a physical defect in the block responsive to differences in reading the page of the NAND memory cells at the first set of read reference levels and the second set of read reference levels being localized to a sub-group of the page of memory cells located at a physical segment of the word line.

A non-volatile storage system comprising:

• a three-dimensional memory structure having blocks containing word lines and NAND memory cells;
• and
• one or more control circuits in communication with the three-dimensional memory structure, the one or more control circuits configured to:
• perform one or more read retries of a group of memory cells connected to a selected word line in a block in the three-dimensional memory structure responsive to a read error using a first set of read reference levels to read the group until a second set of read reference levels are found that succeed in reading the group of memory cells;
• determine whether there is a physical defect in the block based on physical locations of memory cells having a different result when reading the group at the second set of the read reference levels than reading the group at the first set of the read reference levels, including determine which memory cells in the group have a different result when reading the group at the second set of the read reference levels than reading the group at the first set of the read reference levels, the different result being a bit flip, and determine that the physical defect exists in the block responsive to a determination that a first number of the bit flips for memory cells located at a first physical segment of the selected word line is more than a threshold amount greater than a second number of the bit flips for memory cells located at a second physical segment of the selected word line different than the first physical segment;
• and
• retire the block responsive to a determination that the physical defect exists in the block.