Extending a quote by commentator Cory, under normal circumstances "<i>[...] volumes that operate with 20 GB or less of modified data since their most recent Amazon EBS snapshot can expect an annual failure rate (AFR) of between 0.1% – 0.5%, where failure refers to a complete loss of the volume.</i>" (<a href="http://aws.amazon.com/ebs/" rel="nofollow">http://aws.amazon.com/ebs/</a>).