Does that mean I should use both usb 3.0 ports at the same time to connect them? How would this affect overall cpu usage?
Don’t forget that goal is not to ‘archive’ samples but to work with them and realtime stream them on every project, I’m a bit afraid that two external hard drives (even one) will decrease system workflow speed.
No, on the contrary, having two external hard drives is preferable in my experience. There is a limit to how much can be streamed from one disk. There is less of a limit to how much can be streamed to two disks. As I said originally, there are multiple composers I know, using multple Thunderbolt and USB 3 drives to great effect. Originally, before Thunderbolt and USB 3, composers (including myself) were using eSATA to achieve the same thing. External drives are good.
Your CPU is not having a problem grabbing the data from those disks, trust me. What is killing your CPU right now is running your system, and your DAW and your samples all on the same drive, especially one that runs at 5400 RPM!!! You need to spread the workload.
CPU problems, especially for sample-based composers are because of:
Overuse of reverb, particularly NI’s factory reverb which is a resource hog.
Intense scripting. Many of the libraries that are out these days have incredibly complex (in many cases, needlessly complex) scripting that puts an intense amount of pressure on the CPU. Just load up some of the sound design patches from 8Dio / Soundiron, it’s crazy.
Finally, one thing I forgot to mention, and it’s super important.
You are much better off getting a hard drive enclosure and then putting internal drives inside the enclosure, rather than just ‘standard’ external drives. But it’s your call, as this will be more expensive.
Finally, one more brand to consider that I forgot is GLYPH, but they are expensive.