Selecting AWS Storage for MongoDB Deployments: Ephemeral vs. EBS involves understanding the size of your application's working set, which is frequently accessed data that can lead to saturated disk and severe performance degradation if not managed properly. Amazon Elastic Block Store (EBS) volumes are persistent block-level storage attached to EC2 instances, providing durability but higher costs compared to EC2 instance stores, also known as ephemeral storage, which have better performance, decreased cost, and decreased complexity, but data is lost when an instance is terminated. To mitigate this, MongoDB can be configured in a replica set across multiple availability zones, with at least one secondary using EBS volumes for added assurance of data persistence. When using EBS volumes, it's recommended to use Provisioned IOPs (PIOPs) for reliable and predictable performance, as non-PIOPs are subject to noisy neighbor issues, which can cause unpredictable performance dips. Additionally, dedicated throughput through EBS optimized instances is crucial for consistent bandwidth to the EBS volume. RAIDing volumes can also be used for performance or redundancy but requires special consideration of backup strategies. Finally, SSD backed volumes provide better value than magnetic volumes for users of MongoDB due to their ability to handle random IO patterns more effectively.