If you plan on building RAID 5 with a total capacity of more than 10 TB, consider RAID 6 instead.
The problem with RAID 5 is that once the member disk had failed, it is required to read the entire array in order to complete the RAID rebuild. Although the probability of encountering a read error in any particular read operation is very low, the chance of a read error occurring increases as the array size increases. It has been widely speculated that the probability of encountering the read error during rebuild becomes practically significant as the array size approaches 10TB. Although the speculation relies on certain assumption which is not likely to be true (we'll have a writeup on that later), consider being better safe than sorry.
RAID 6, being capable of correcting two simultaneous read errors, does not have this problem.