Maintenance operations for multi-level data storage cells

The present invention relates to a maintenance operation of the multi-level data storage unit. Including computer software for a system and method for reading data from the flash memory unit (124) relates to the detection voltage from the storage unit group. The group of memory cells having associated metadata for error detection (605), and each memory cell stores a voltage which represents a data value selected from a plurality of possible data values. Every possible data values ​​corresponding to a plurality of non-overlapping analog voltage range in a range. A storage unit having uncertain data values ​​is based on the detected voltage to the identified (610). For storage unit with uncertain data values, its alternate data value is to be determined (615). Combination of alternative data values ​​will be selected (625), and uses the metadata storage unit is associated as well as alternative data value combinations selected to perform error checking (635).