Just to make it clear. raid-5/6 mdadm arrays does the right thing when repairing/checking/scrubbing data. It writes the correct data if one of the drives has a corrupted block.
https://raid.wiki.kernel.org/index.php/RAID_Administration
How often does this happen? According to what I have been reading, without ECC RAM and without ZFS, your machines get roughly one corrupt bit per day. In other words, that could be a few corrupt files per week.