I am excited to be able to tell you about an entire new feature, a feature so new that it doesn't even have a proper name, and that you can't use just yet. But you can read about it and you can start thinking about the best way to incorporate it into your system architecture.
If you have taken a close look at Amazon EC2, you know that the instances are ephemeral. The instances have anywhere from 160 GB to 1.7 TB of attached storage. The storage is there as long as the instance is running, but of course it disappears as soon as the instance is shut down. Applications with a need for persistent storage could store data in Amazon S3 or in Amazon SimpleDB, but they couldn't readily access either one as if it was an actual file system.
As you can read in our forum post, we've been working on addressing this.
In the same way that your running EC2 instances, your Elastic IP addresses, your S3 buckets and your SQS queues can be thought of as items contained within the scope of your AWS account, our forthcoming persistent storage feature will give you the ability to create reliable, persistent storage volumes for use with EC2. Once created, these volumes will be part of your account and will have a lifetime independent of any particular EC2 instance.