In a storage device, the term “non-recoverable read error”, or NRRE, refers to the failure of a read operation to return the requested data after exhausting all means to recover it. These may also be called “unrecoverable read errors” or “uncorrectable bit errors”. There are situations where such a non-recoverable  error may occur on a read operation, but the data location itself is still capable of storing data. Therefore, if data is subsequently written to the location, the error condition may be cleared.

A non-recoverable read error is a data loss event at the device level. Causes are varied and depend on the type of storage device. Examples include when the number of bit errors exceeding the correction power of the error correction code (but not the detection power!), or when a data signature doesn’t match.