A method is disclosed to preserve data integrity during loss of power to an information storage and retrieval system. Applicants' method converts a plurality of sectors having a first sector format to a plurality of sectors having a second sector format. If a power failure warning is received during the sector format conversion process, the method prefetches the next second sector, overlays the next first sector onto part of all of that prefetched second sector, and saves the newly-written second sector before loss of utility power. After restoration of utility power to the information storage and retrieval system, Applicants' method writes that newly-written second sector to an information storage medium.