The AWS Storage Gateway is a service connecting an on-premises software appliance with cloud basedstorage to provide seamless and secure integration between an organization's on-premises ITenvironment and AWS's storage infrastructure.
AWS Storage Gateway billing is as follows.
Volume storage usage (per GB per month):
You are billed for the Cached volume data you store in Amazon S3. You are only billed for volumecapacity you use, not for the size of the volume you create. Snapshot Storage usage (per GB permonth): You are billed for the snapshots your gateway stores in Amazon S3. These snapshots arestored and billed as Amazon EBS snapshots. Snapshots are incremental backups, reducing yourstorage charges. When taking a new snapshot, only the data that has changed since your lastsnapshot is stored.
Virtual Tape Library usage (per GB per month):
You are billed for the virtual tape data you store in Amazon S3. You are only billed for the portion ofvirtual tape capacity that you use, not for the size of the virtual tape.
Virtual Tape Shelf usage (per GB per month):
You are billed for the virtual tape data you store in Amazon Glacier. You are only billed for theportion of virtual tape capacity that you use, not for the size of the virtual tape.
Reference:
https://aws.amazon.com/storagegateway/faqs/