  The three traditional failure classes are system, media, and transaction
failures. Sometimes, however, modern storage exhibits failures that differ from
all of those. In order to capture and describe such cases, single-page failures
are introduced as a fourth failure class. This class encompasses all failures
to read a data page correctly and with plausible contents despite all
correction attempts in lower system levels. Efficient recovery seems to require
a new data structure called the page recovery index. Its transactional
maintenance can be accomplished writing the same number of log records as
today's efficient implementations of logging and recovery. Detection and
recovery of a single-page failure can be sufficiently fast that the affected
data access is merely delayed, without the need to abort the transaction.
