The effect of a reread on data reliability

When a disk drive sector cannot be reliably decoded on a first try because of excessive errors, the sector may be read a second time. We analyze the effect of rereading the sector on data reliability. To this end, we separate noise sources into two classes: repeatable and nonrepeatable. We derive analytical expressions that predict the data reliability improvements due to reread. We show that, under reasonable assumptions, significant enhancements are achieved by a reread