A couple of things here.
First of all -- if you plan to turn off your Terra and then download HD content to your Alto, you should delete the HD content from your Terra first! Otherwise, when you turn the Terra on again, you will have two HD copies of those movies on your system, and no way to pick which one to delete. (If you've already done this, then my suggestion would be to turn the Alto off, then turn the Terra on, delete the HD movies, and finally turn the Alto back on again.)
Lastly, just as an FYI since it was mentioned above, if you remove a server from a system, any downloaded content on that server becomes deauthorized and unplayable, but it remains on the hard drive(s). If you later add the component back to the system, since your ownership of those movies is stored in the cloud, the system will quickly recognize that you own the content on that component, and they will become authorized and playable again. For the specific scenario discussed here, just powering the component down is easier, though.
I'm sorry that this has become a hassle. The download design for a system with a Terra and a player with storage was chosen so that we would favor the high-performance storage in the Terra, which allows the system to support more simultaneous movie playbacks and so on. The downside is, as you've discovered, that once storage fills up in the Terra. The common use case we imagined for this was a Terra plus a Strato. So even after the Terra filled up, you'd still be able to download 4K to the Strato's storage. Terra + Alto is a less common configuration, and as you've found, it has this caveat with 4K content once the Terra fills up.
First of all -- if you plan to turn off your Terra and then download HD content to your Alto, you should delete the HD content from your Terra first! Otherwise, when you turn the Terra on again, you will have two HD copies of those movies on your system, and no way to pick which one to delete. (If you've already done this, then my suggestion would be to turn the Alto off, then turn the Terra on, delete the HD movies, and finally turn the Alto back on again.)
Lastly, just as an FYI since it was mentioned above, if you remove a server from a system, any downloaded content on that server becomes deauthorized and unplayable, but it remains on the hard drive(s). If you later add the component back to the system, since your ownership of those movies is stored in the cloud, the system will quickly recognize that you own the content on that component, and they will become authorized and playable again. For the specific scenario discussed here, just powering the component down is easier, though.
I'm sorry that this has become a hassle. The download design for a system with a Terra and a player with storage was chosen so that we would favor the high-performance storage in the Terra, which allows the system to support more simultaneous movie playbacks and so on. The downside is, as you've discovered, that once storage fills up in the Terra. The common use case we imagined for this was a Terra plus a Strato. So even after the Terra filled up, you'd still be able to download 4K to the Strato's storage. Terra + Alto is a less common configuration, and as you've found, it has this caveat with 4K content once the Terra fills up.
