The limits are on the number of simultaneous failures. Data is safe provided that too many errors do not accumulate before they can be detected and corrected.

The limits are on the number of simultaneous failures. Data is safe provided that too many errors do not accumulate before they can be detected and corrected. This is fundamental fact: no real storage system can tolerate an unbounded number of simultaneous errors without an unbounded number of space for replicas. You can control the number of allowable simultaneous errors by tuning redundancy settings (the trade off is space efficiency vs. probability of data loss). It is straightforward to put in place an automated process to guarantee that errors are detected within some finite period of time.