I really like BTRFS, that's why I write so much about it. But there are some issues with it. BTRFS is based on the copy-on-write principle but this can create some real troubles with virtualisation or databases. Therefore I will explain in this article how to disable cow.
Btrfs has it's builtin tool for displaying IO stats on devices. Beside this it's good to scrub the RAID from time to time.
I had some problems with mdadm in the past and Btrfs seems to be a good alternative for it. I will remove one disk of my mdadm-array and turn it into btrfs. Then I will copy all my data on my btrfs using Compression. Of course I will backup my data. Then I will remove my mdadm-array and add the hard-disk to my btrfs, convert the filesystem to a Raid1 and create a Subvolume on it for all my /home-directories. I am courious how it works...