By creating a snapshot, we are creating a point-in-time copy of the whole volume and storing it on the Amazon Simple Storage Service (S3), which we will discuss in detail in Chapter 7, Understanding Simple Storage Service and Glacier. Snapshots are incremental copies of the EBS volume, meaning that only the blocks on the storage device that have changed since your most recent snapshot are stored to the snapshot. Although this sounds like a good way to perform traditional backups of an EC2 instances storage, we need to be aware that snapshots need to be integrated with a backup procedure, script, or backups software that sits within the instance and will commit all the outstanding I/O operations to disk before the snapshot is started. If there are any pending I/O operations that are left out of a snapshot, it could cause the data that's being copied to the snapshot to be of no use when we try to restore it.