Where is my snapshots' used space?

[winnielinnie]

@swc-phil

I thought that I embraced basic concepts of ZFS snapshots . And that used space of snapshot is the amount of data exclusively contained/referenced by this snapshot. If my understanding is correct, all snapshots combined that still contain .purgeable 400GB file must use (at least) 400GB of space. Yet they use just a few GB. OTOH, the dataset itself shows correct 756 GB usage.

This might help you better understand what you’re observing.

The last part addresses this “math doesn’t add up” phenomenon of ZFS snapshots.