Where is my data stored?

Your data, encrypted, is stored on Amazon's Simple Storage Service (S3), which is a convenient, reliable, and widely understood platform for storage.

Data is replicated according to the following policy decribed in Amazon's Overview of Security Processes:

Data stored in Amazon S3, Amazon SimpleDB, or Amazon Elastic Block Store (EBS) is redundantly stored in multiple physical locations as part of normal operation of those services and at no additional charge. Amazon S3 and Amazon SimpleDB provide object durability by storing objects multiple times across multiple Availability Zones on the initial write and then actively doing further replication in the event of device unavailability or detected bit-rot.