Sadly, like any other option, ZFS can't magically create more storage space. People usually do something like keep hourly snapshots for a week, weekly snapshot

Sadly, like any other option, ZFS can't magically create more storage space. People usually do something like keep hourly snapshots for a week, weekly snapshots for a few months and monthly snapshots for a year. My policy with data is similar to real life things: if I didn't notice it gone for a whole year then I probably don't need it. Are you perhaps hinting at using offline storage for long-term archival? What options are there? Tape? As far as I know, keeping hard disks online is still the best way to achieve this, sadly.