Backing up to local RAID is nice, unless you're using local RAID as your primary storage in the first place, like we do. I'd looked into using a combination of AWS S3 Glacier and FUSE (s3fs?) for rigging snapshots to S3 via btrbk but it seems the semantics of Glacier don't align all too well, and backing up 40 TB+ worth of WAL on a monthly to S3 is more expensive than it should be unless you're using that storage class.