Additionally, assuming your block data is being hash-addressed, i.e. not changing the S3 objects once they are in S3, adding CloudFront in front of your buckets

Additionally, assuming your block data is being hash-addressed, i.e. not changing the S3 objects once they are in S3, adding CloudFront in front of your buckets may go a long way to increasing that percentage. However, its SLA is a little more involved (for better or worse): http://aws.amazon.com/cloudfront/sla/ http://aws.amazon.com/cloudfront/sla/ I'm not accessing S3 from EC2, though, so another benefit for me was it brought my S3 network costs way down.