How to manage memory consuming by FinalCut editor?

It depends on the media you’re using and the complexity of what you’re doing. If you are dropping frames during playback it’s usually a problem with the drive or connection. For HD media you need a fast drive and connection. A 7200rpm drive with USB 3 is the minimum. Ideally the external drive should be a SSD with USB-C or Thunderbolt 3. SSDs are much faster and more reliable than spinning drives.

As a small addition to what Tom said: SSD are not that expensive anymore; an external 500 GB may be just what you need; and use the HD you already have for archiving once you are done with a production.

Also: the most common reason why a disk fills up real fast is Optimized and Proxy Media.

Make sure that you delete generated files, and turn off the creation of these things on import.

The optimized version of a clip may take ten times the space of the original version.

I think it is, though I don’t know the specifics of the system or the drive you’re using. I don’t know how long your m are or how much media you use, but an SSD that was large enough with at least 20% free space would be best. Personally I’m not to going to buy a spinning drive again.