The reason I suggested it is because thin volumes are well understood, so the issues are straightforward... and it's been implemented in many products (lvm; vir

The reason I suggested it is because thin volumes are well understood, so the issues are straightforward... and it's been implemented in many products (lvm; virtually every san; xenserver & vmware; etc). So there really shouldn't be many surprises if amazon were to implement it. And yes, trim is used to mark blocks as free. Honestly, it's so widespread, I would be surprised if Amazon weren't already using it to over-commit ebs.