The way thin provisioning normally works (e.g. on ZFS or LVM) is that only non-zero blocks are stored; an unstored block is read as zero; a block written as zer

The way thin provisioning normally works (e.g. on ZFS or LVM) is that only non-zero blocks are stored; an unstored block is read as zero; a block written as zeroes could be "unstored". It doesn't matter whether a block of zeroes is stored or not: it still reads as zero. So a cloud provider only needs to store non-zero blocks, and thus doesn't need to provision the full capacity to back a volume. As to whether EC2 does this I don't know - based on your observations they may not. I think it's an interesting way to build a storage product like Glacier, even if Amazon may have chosen to do something different.