> I don't know if ZFS supports variable compression levels (maybe per dataset) > Thus it's possible to use a higher level (high compression ratio, slower speed

> I don't know if ZFS supports variable compression levels (maybe per dataset) > Thus it's possible to use a higher level (high compression ratio, slower speed, more CPU and RAM) for e.g. an initial archive. And later use a lower level (or even no compression) when doing updates. yup. works the same in ZFS. you can change the compression setting any time you like, for future writes.