I've done thorough testing on random read/write performance of ephemeral vs EBS, and I can tell you that EBS is waaaay better in the case of random IO. I can attest to the accuracy of the random IO performance in one of the references from the post:<p><a href="http://victortrac.com/EC2_Ephemeral_Disks_vs_EBS_Volumes" rel="nofollow">http://victortrac.com/EC2_Ephemeral_Disks_vs_EBS_Volumes</a><p>Amazon even says this on their page (also referenced by Gabriel).<p>Joe Stump's article might lead you to believe the ephemeral and EBS are equal for random IO, but Joe only tested on a RAID0 config with two EBS volumes.<p>In general, even with the best instances under the best circumstances, you won't crack 2K iops/sec on ephemeral RAID0 with four drives.<p>EBS, on the other hand, with 8 volumes configured in RAID0 will exceed 24K random reads/sec and 12K random writes/sec. The reads are so much higher because EBS is mirrored.<p>The downside with EBS is you can see worse performance when there are noisy neighbors. I've seen performance drop 50-70% for hours at a time on m1.large because of network card contention, but you can avoid this when on larger instances (m1.xlarge or m2.4xlarge do the trick).<p>Sequential IO is another matter. I haven't thoroughly compared, but I believe in this case things are more even.<p>Performance aside, there is something to be said for removing dependencies on a complex system like EBS. It also frees up network bandwidth and provides quite a bit of storage without the $0.10/GB cost of EBS. If iops isn't a problem and you plan on replicating, then ephemeral can be a big win.