The Amazon servers have local disks physically attached. They are wiped between customers, on machine failure etc hence "ephemeral". The EBS (elastic block storage) is accessed as a disk but is over the other end of a network connection. Amazon does more to ensure the contents are available and durable (eg replication, backup to S3). The problem with EBS is that performance especially latency is highly variable and unpredictable.
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By local storage, do they mean they are running their DB disks on physical hardware, but the database servers still on EC2?
The Amazon servers have local disks physically attached. They are wiped between customers, on machine failure etc hence "ephemeral". The EBS (elastic block storage) is accessed as a disk but is over the other end of a network connection. Amazon does more to ensure the contents are available and durable (eg replication, backup to S3). The problem with EBS is that performance especially latency is highly variable and unpredictable.