A storage gateway serves as an interface between processes on a customer network and a service provider. The storage gateway is located on-premise with the customer processes. To customer processes, it appears that data is stored locally. However, the storage gateway interfaces with a remote storage service to store the data. For cached gateways, the primary data store is a remote data store, while frequently accessed data may be locally cached by the gateway. Reads may be satisfied from the local cache or from virtual data storage; writes are handled so as to appropriately update data blocks in the local cache and/or in virtual data storage. For shadowing gateways, the primary data store is the local data store; reads are passed through to a local data store, and writes are shadowed to virtual data storage as well as being sent to local data store.