RAID scrubbing is an important maintenance task to prevent the emergence of inconsistencies on RAID arrays (cp. http://en.wikipedia.org/wiki/Data_scrubbing#RAID). Although the kernel provides the necessary interfaces to start scrubbing, it is rather complicated to automate this task considering all possible pitfalls. There is a script available solving this problem: https://github.com/fukawi2/raid-check This script is available in several distributions via the package managers, but up to now there seems not to be an ebuild available.
In the tree as sys-block/raid-check