Parts fail all the time. The problem with hardware raid is you need a compatible controller or none of the data can be read even though it is still on the physical disks. Computer hardware is often only made for a few months before there is a new model and so you are risking that the manufacture really made the new model work with what you have. That is assuming the manufacture doesn't go out of business which could happen without warning. \

Also, if hardware breaks that is often a good excuse to replace it - odds are better hardware is available for the same price and sometimes a lot less $ - with hardware raid you are stuck paying whatever price they charge.