Spark called it. crc32 is a cheaper operation than MD5, roughly %40 less CPU if I remember correctly. That makes the election hash iRule scale much better. But the downside to crc32 is that it often results in collisions. Practically speaking, this means that you will get an uneven distribution. If you have a bunch servers, some will get as much as %80 more than others even after a normalization of millions of queries. MD5 is meant to be cryptographically secure, hence very few collisions, which means for use as a load balancing algorithm, near perfect distribution of queries across servers.