How durable is Amazon S3?
Amazon S3 Standard and Standard - IA are designed to provide 99.999999999% durability of objects over a given year. This durability level corresponds to an average annual expected loss of 0.000000001% of objects. For example, if you store 10,000 objects with Amazon S3, you can on average expect to incur a loss of a single object once every 10,000,000 years. In addition, Amazon S3 is designed to sustain the concurrent loss of data in two facilities.
As with any environments, the best practice is to have a backup and to put in place safeguards against malicious or accidental users errors. For S3 data, that best practice includes secure access permissions, Cross-Region Replication, versioning and a functioning, regularly tested backup.
How is Amazon S3 designed to achieve 99.999999999% durability?
Amazon stores your objects on multiple devices across multiple facilities in an Amazon S3 Region. The service is designed to sustain concurrent device failures by quickly detecting and repairing any lost redundancy.
Amazon S3 also regularly verifies the integrity of your data using checksums.