A timeout means your client isn't reading fast enough.
JMeter isn't reading the response data fast enough, so the connection sits idle long enough that it idle times out and disconnects.
We test with 800MB and 2GB files regularly.
On using HTTP/1.0, HTTP/1.1, and HTTP/2 protocols.
Using normal (plaintext) connections, and secured TLS connections.
With responses being delivered in as many Transfer-Encodings and Content-Encodings as we can think of (compressed, gzip, chunked, ranged, etc.).
We do all of these tests using our own test infrastructure, often spinning up many many Amazon EC2 nodes to perform a load test that can sufficiently test the server demands (a typical test is 20 client nodes to 1 server node)
When testing large responses, you'll need to be aware of the protocol (HTTP/1.x vs HTTP/2) and how persistence behavior of that protocol can change the request / response latency. In the real world you wont have multiple large requests after each other on the same persisted connection via HTTP/1 (on HTTP/2 the multiple requests would be parallel and be sent at the same time).
Be sure you setup your JMeter to use HTTP/1.1 and not use persisted connections. (see JMeter documentation for help on that)
Also be aware of your bandwidth for your testing, its very common to blame a server (any server) for not performing fast enough, when the test itself is sloppily setup and has expectations that far exceed the bandwidth of the network itself.
Next, don't test with the same machine, this sort of load test would need multiple machines (1 for the server, and 4+ for the client)
Lastly, when load testing, you'll want to become intimately aware of your networking configurations on your server (and to a lesser extent, your client test machines) to maximize your network configuration for high load. Default configurations for OS's are rarely sufficient to handle proper load testing.
