I understand the storage servers are raid-6. Can I ask if you've had any drive failures and if yes, any problems rebuilding? Does it happen often? Have you had any 2-drive failures? I think it's good if you've had some failures and successful rebuilds. Drives do fail so if you've had it happen already, it means the raid system is working and it's good to know that.
Where I used to work we replaced about 1 drive per day on average in our small DC.