Is Amazon SimpleDB more reliable/available than DynamoDB?

Question

This question is not about a general comparison between the two but more specifically focussed on high availability and reliability. From amazon's documentation about this:

SimpleDB

Amazon SimpleDB automatically creates multiple geographically distributed copies of each data item you store. This provides high availability and durability – in the unlikely event that one replica fails, Amazon SimpleDB can failover to another replica in the system.

and

DynamoDB

Amazon DynamoDB is a fully managed NoSQL database service that provides fast and predictable performance with seamless scalability. The service runs across Amazon’s proven, high-availability data centers. The service replicates data across multiple facilities in an AWS Region to provide fault tolerance in the event of a server failure or Availability Zone outage.

So, in relative terms, is one more reliable than the other?

Answer 1

Both services are highly available and reliable. The main difference being performance and cost.

SimpleDB is a NoSQL database as well is DynamoDB, DynamoDB however is designed for single digit millisecond fast performance under any amount of load. SimpleDB is also going to be fast but its not designed for large datasets.

As a result billing for DynamoDB is much more expensive. You must also "reserve" usage for dynamoDB its not billing you on how many requests you make, its billing you on how many you think you're going to make.

DynamoDB - Large datasets and fast performance

SimpleDB - Small / Medium datasets and cheaper