Zero-one balance management in a solid-state disk controller

A storage system comprising:

• a plurality of storage devices, wherein the storage devices are coupled to a non-volatile memory;
• and
• a plurality of storage controllers in communication with the plurality of storage devices, the plurality of storage controllers configured to
• scramble data to be written to a portion of the non-volatile memory to produce scrambled data having a known statistical average number of zero bits and a known statistical average number of one bits,
• write the scrambled data to the portion of the non-volatile memory, wherein the writing comprises encoding the scrambled data with an error-correcting code (ECC) encoder and writing the encoded scrambled data to the portion of the non-volatile memory, and wherein the ECC encoder adds at least one byte to the scrambled data, the at least one byte having the known statistical average number of zero bits and the known statistical average number of one bits,
• subsequent to the write, read the portion of the non-volatile memory,
• compute a disparity between a number of zero bits and a number of one bits in data read from the portion of the non-volatile memory,
• determine a threshold voltage for a subsequent read of the non-volatile memory based at least in part on the disparity,
• re-read the portion of the non-volatile memory using the threshold voltage, and
• prior to the re-read, decode the data read from the portion of the non-volatile memory with an ECC decoder to determine that the data read from the portion of the non-volatile memory is uncorrectable.