Preventing Snapshots

While it's not intuitive, you can delete snapshots by selecting the settings "gear" icon for the share on the Shares page, selecting "Recover", and then right-clicking on the snapshot name.  One of the options will be Delete.  After you do the delete, the space will be recovered in the background, so give it some time.  If nothing is recovered, then there is another shapshot that includes all the same data or there is nothing in the snapshot that's not still active.

If you have a share with a lot of "churn", snapshots can fill the NAS in a hurry.  Periodic PC backups that are not incremental can be especially troublesome.  Frequent volume defrags can also cause snapshots to use a lot of space.

You can disable snapshots for troublesome shares by using the same gear icon and sellecting Settings, then the Snapshots tab.  There, you can turn them off or you can go to Custom snapshots where you have more control over when they are taken and their retention.  If you are starting over (which you probably don't need to do, maybe I stopped you in time), you can also select snapshot options when you create the shares.

BTW, the NAS will start to delete old snapshots as you start to run out of free space.  But it's not especially smart about how it does that -- it just deletes the oldest without looking at the largest.  That's why using custom snapshots can help make sure the snapshots for shares on which you need them the least are the first to go.  You do also have some control over this "pruning" process, but only by volume, not share.  On the Volumes page, use the gear icon for the volume and select Settings, then Snapshot Pruning.  There, you can specify the amount of used space at which it will start deleting them.  Less than 90% isa not recommended, and 80% is better (and, I think, the default).  It absolutely must leave enough space for what is your typical largest uplkoad in a few hours, as the snapshot pruning and free space recovery can take a while.

Most of this is covered in the manual.  A NAS is a lot more complex than a simple USB drive cage, and it's often a good idea to take a second (or even a third)  look at the manual after you've owned the NAS for a while.  First time through, a lot may not sink in.  Netgear also publishes online manual updates that cover new features of OS updates, so don't just stick with the one that came with your NAS.  I'm not saying that this necessarilly applies to you, but a "we don't need no stinking manual" attitude is definately a minefleld.