Two reasons come to mind: * the failure rate of an EBS volume (assuming a bug-free EBS software stack!) should be less than any one spinning disk * these mach

Two reasons come to mind: * the failure rate of an EBS volume (assuming a bug-free EBS software stack!) should be less than any one spinning disk * these machines don't have disk space set aside for copying the root volumes to them from S3 to boot. (There's a 10GB limit, and to allow for this to be somewhere, you'd have to have another SSD, or partition the existing ones.) There's a good blog post about it on Rightscale: http://blog.rightscale.com/2012/11/02/new-ec2-instance-types-and-coordinated-failures-in-the-cloud/ http://blog.rightscale.com/2012/11/02/new-ec2-instance-types... esh's "You Should Use EBS Boot Instances" also lays out a number of good reasons to use EBS for boot: http://alestic.com/2012/01/ec2-ebs-boot-recommended http://alestic.com/2012/01/ec2-ebs-boot-recommended You at least have two 120GB ephemeral SSDs to play with when you're running - a luxury you don't have on the new M3 classes.