Sorry for getting back to you so late.
@Trin: Your config sounds ok. You will have to play with it for a bit to gain experience with your solution.
@BIGNOOKIE: Raid6 has two advantages over Raid10: capacity and resilience. Raid10 obviously gives you more performance. I had to stop and think for a moment why Raid6 is more resilient, but the reason is this: When a disk failed and is replaced, Raid10 has to copy the contents of one disk to the new disk. All other disks of the Raid10 are idle during recovery. If that source disk has a single read error, your data is compromised. Raid6 on the other hand can handle a read i/o error during rebuilding (in fact, it can handle another entire disk failure during rebuilding).
Hence, from a resilience perspective, Raid10 is only marginally better than Raid5 (roughly n-1 times more resilient than Raid5, where n is the number of disks in your raid). Raid6 is order of magnitudes more resilient than Raid5. Let's do some math, cause I feel like itRaid10
According to the spec sheet of a WD Red Pro Disk, it has a unrecoverable bit read error rate of <10 in 10^15 bits. I'll use 10^15 for arguments sake, making the disk slightly more reliable than the spec sheet says it is. A 6TB disk has about 5*10^13 bits. Assuming failures happen uniformly at random, then each read bit has a failure probability of 1/10^15. The chance of success hence is (1 - 1/10^15). Thus, the chance of successfully reading an entire 6TB disk is (1 - 1/10^15)^(5*10^13) = ~95.1%.
It follows that your Raid10 rebuild fails in more than one of twenty cases
using 6TB WD Red Pro disks (more because we've taken a slightly lower error rate than what the spec sheet says).Raid6
This is a little harder to calculate, because if a bit cannot be read from one disk, the other disks can correct this if they successfully read the raid chunk (usually 512KB or something like this), but bear with me
Let's start with the simple thing: The chance of a Raid6 recovery succeeding without hitting a single bit read error. This is essentially the same as before, only we need to read a lot more data (n-1 disks instead of just one as in the Raid10 case). I use a Raid6 over 12 disks in this example (so we need to read the data off 10 disks), hence:
(1 - 1/10^15)^(10*5*10^13) = 60.67%
Ouch. So the probability of successfully recover such a large array without a single bit read error is quite low. This is the reason why people say Raid5 is dead
(this figure above is the probability of recovering a Raid5 over 11 disks without a bit read error).
But we're Raid6. So in case we do hit a bit read error on one disk, we can recover from that if the remaining 10 disks can read their chunk of ~500KB in which the read error occurred. So:
(1 - 1/10^15)^(10 * 500 * 1024) = 99.99999948%
(that's six 9s after the dot).
So the chance of a successful recovery after a bit read error is tremendously high. Combining the two figures, the chance of a Raid6 recovery not failing due to a bit read error is:
(1 - 1/10^15)^(10*5*10^13) + (1-(1 - 1/10^15)^(10*5*10^13)) * (1 - 1/10^15)^(10 * 500 * 1024) = 99.9999998%
(again, six 9s after the dot).
Note: We've ignored the chance of the entire disk failing, because it's much harder to get statistics for that. But even then, Raid6 will do much better than Raid10.