"How to go about doing that" was more in reference to the logistics of creating somewhere to move the data to than actually how to move it, because Windows Explorer drag-and-drop is a thing.
That means setting up a SMB share and leaving a machine on for hours while you transfer files from a dataset or a pool to another. Not ideal, but possible.
Assuming we omit "permanently deleting data" from the list of possible solutions, it all involves spending money as I have zero spare drives at present.
From the informations you gave us I don't see any other options than:
- deleting some files from the pool
- expanding the pool by adding another vdev
- creating a new pool and moving some files there
The first option means either deleting data (I'd start from the snapshots) or moving some files to other places such as another machine, the cloud or an external drive; this should cost you little or no money depending on what you have.
The second option means doubling your space and, as Kris already noted, costs a considerable sum of money.
The third option is to buy two big enough drives to create a new pool and move some of your data there; it could cost less than adding another vdev to your main pool, but it comes with less flexibility and the need for a reogranization of your storage and sharing strategy.
Which makes it all the more important to have some sort of plan here.
Nope, you should have had a plan
before reaching this point or rather you shouldn't have let it reach this point: you should either have monitored better your available space (TN tries to tell you this in quite a few ways) or choose a different pool layout when you assembled your system (like mirrors), maybe both. Now there isn't much we can do without spending money.
I'd also like to point out that the tone I'm picking up from of a few of your replies isn't exactly going to make people address your issue; I understand your frustration, but please be aware of that since it's going to hurt you in the long run if it escalates.
