Erik:
I go along with what you say if regarding the storage of 3 copies. There are always trade offs though related to available memory space, time to perform storage updates, etc.

I have found from years of practical experience though that two copies of small data sets (1 - 20 bytes) that an 8 bit xor-CRC is both efficient on storage usage and quick to calculate. In some applications I have used 93C46 that contained up to 15 counter / accumulators, stored 2 times each, that took 2 locations per counter (4 per copy) for a total of 15*4=60 locations out of 64 in the part. Each counter in this application can have 3 bytes value and 1 byte xor-CRC.
Mike