All gateways are Virtual appliance (VM image) that can be downloaded and installed on a hypervisor (VM ware VSXi or MS Hyper-V) locally in your data center.
Three types of storage gateways (acronym FTV File Volume Tape) are available to choose from:
File Gateway (NFS Network File System mounts) stores flat files in S3 such as images, PDF/doc/xls files etc.
Amazon S3 and Amazon Glacier cloud storage.
File gateway offers an NFS mount for S3 with local caching.
It can be used for on-premises applications, and for Amazon EC2-resident applications that need low-cost file storage.
No storage on premises (Only cache)
No limit on size
Volume Gateway (iSCSI) provides virtual hard disks. Can be used as a block storage to install OS or databases such as MySQL/SQL Server etc.
Stored Volumes: All data is stored on premises and snapshots are backed up on S3 . Volume size: 1 GB to 16 TB
Cached Volumes: S3 is used as primary storage. Only most recently used data is cached on premises. Volume size: 1 GB to 32 TB
Tape Gateway uses VTL (Virtual Tape Library) protocol to backup virtual tape archives on S3 Glacier.