Most errors are detected by checksums or hashes, so measure that across all your hardware (client requests, network hops, server RAM) and estimate how often you

Most errors are detected by checksums or hashes, so measure that across all your hardware (client requests, network hops, server RAM) and estimate how often your checksum should have collided and let an error slip by. Granted, it's pretty rare to work on a big enough system to have solid data on this.