On EC2, most of the larger current generation instances have multiple SSD devices. To take advantage of the combined size of these for applications like nosql databases that store large amounts of data, I've been combining them with software raid 0 or 10 using mdadm.
It takes forever when launching new instances though, for instance to run the initial raid10 sync on an i2.4xlarge instance takes several hours to complete.
Is there any way to speed this up? Is it possible to save an AMI after running the initial mdadm sync that will include all the ephemeral disks in the same raid configuration when it lauches?
I haven't used custom AMI's much but from reading the docs it sounds like both instance store backed and ebs backed AMI's only include a snapshot of the root volume.