As we look at privacy of big data within any cloud, on premise, or mixed, we need to realize that the amount of data could be so large that retroactively redacting data may be itself a big data problem and that redacting well defined PII is a possibility on ingest as well as using tools like DataGuise to redact, encrypt, tokenize, etc. such data retroactively can be accomplished as another big data task, but that only handles well known PII. How do we handle derived PII?