A btrfs raid1 means mirroring all data and meta data on file system level. If you ever found some of your data lost after a btrfs scrub, you might know this output:
scrub status for <UUID>
scrub started at Thu Dec 25 15:19:22 2014 and was aborted after 89882 seconds
total bytes scrubbed: 1.87TiB with 4 errors
error details: csum=4
corrected errors: 0, uncorrectable errors: 4, unverified errors: 0
If you happen to have free space on a spare disk left, you can circumvent these problems via a btrfs raid1 on filesystem level. The following article will help you migrate.