[danielrhodes]

What's the failure rate of EBS versus having direct access to physical disks? My guess is that at scale, it's probably similar.

Although you would hope that the storage components of AWS's cloud were highly reliable, I think the main benefit is not single instance reliability but being able to recover faster because of quickly available hardware.

[bmurphy]

I don't have solid numbers, just some experience using this. Ephemeral drives outright fail more often than EBS volumes, however, EBS volumes suffer performance degradation significantly more often than ephemeral drives. EBS volume performance is HIGHLY variable, at all times of day, no matter what load you throw at it. Ephemeral drives are very consistent most of the time.

Both types of drives CAN and DO fail, so RAID-10, fail over, and replication are a must have.