EC2 (local) instance storage

Just to be clear, there are two different ways of initializing storage: root filesystems are created from a full disk image that specifies every block, so there are no uninitialized blocks to worry about, while non-root instance storage and fresh EBS volumes are created in a blank state, returning zeros for every block.

It's well documented that fresh EBS volumes keep track of touched blocks; to get full performance on random writes you need to touch every block first. That implies to me that they don't even allocate the block on the back end until it's written to.

Not sure how instance storage initialization works, though.