How about block level checksums? Can LVM do that as well? Or is there some other way? ZFS dedup takes 320 bytes of RAM per unique block "record". So 1TB of RAM

How about block level checksums? Can LVM do that as well? Or is there some other way? ZFS dedup takes 320 bytes of RAM per unique block "record". So 1TB of RAM is enough to dedup only a bit over 6 TB worth of unique blocks, when using a block size that works well with virtual machines — 4 kB. One can of course use larger ZFS record size than 4kB. But virtual machine dedup savings drop very sharply as a result if record size does not match virtual machine filesystem block size and alignment. This happens, because there are exponentially more different combinations how 4 kB blocks can be arranged inside a bigger record size. It's painful to format all virtual machine images to use say 64/128 kB filesystem block size to be able to efficiently use larger ZFS record size dedup. I understand VDO dedup requires significantly less memory and uses only 4 kB blocks for dedup. This is ideal for VM storage application.