The "sleep 10 seconds" solution isn't robust enough. Consider if you have created a snapshot on the filesystem. That snapshot has to keep hold of all the data,

The "sleep 10 seconds" solution isn't robust enough. Consider if you have created a snapshot on the filesystem. That snapshot has to keep hold of all the data, so when you delete files, the amount of free space doesn't change. A loop with "sleep 10 seconds" is likely to delete every single file in the filesystem in an attempt to get that desired amount of free space. A very common thing to do with ZFS is to have automatically rotating snapshots, so that you can go and retrieve a file that you accidentally deleted or changed, without having to go to the backups. In this case, the space is freed when the last snapshot containing those files is rotated away, which could be day or a week later, depending on how it is set up.