Check out Avere systems.  They have a clustered NFS appliance that you can spin up in EC2, which translates back-end S3 object storage into NFS for your clients.  It supports between 3 and 50 nodes, and uses local RAM and SSD cache to accelerate performance.  Avere has also been in the NAS acceleration&#x2F;caching business since 2008, so their product is very mature.