If you want to be 100% certain you HAVE TO pull the disks one at a time and let them rebuild in between.
Do NOT trust the status given to you by your raid controller or any other piece of hardware/software.
I just had one disk die in my RAID 1 + hotspare setup and my Dell 2650 server with Perc 3/Di raid controller and the data went back in time 5 years!!!! (the server has been in operation for 6 years no and was due to be de-commissioned in the next few weeks)
It turns out that RAID broke 5 years ago and everything was being done on one disk only.
Even though all BIOS and other messages from the raid controller, Dell Openmanage software, etc. gave me a green light on its status, it wasn't actually doing what it said it was doing.