The answer here is actually a faster hard drive. The data that gets loaded into RAM is only that which the instrument needs immediately, everything else is streamed from the hard disk on demand. When you see the disk indicator turning red it means the hard drive cannot keep up and when you likely need is to consider an SSD to store the samples on - some of our heaviest users actually put different libraries across different SSDs. Some even store separate parts of the same library on different SSDs.
Additionally, in Kontakt, you can try tweaking a couple of settings.
Look in the preferences for Memory > Instrument Preload Buffer size and increase it if you have a lot of RAM but are suffering from Hard Drive slowness. You could also consider increasing the latency as described here: https://support.native-instruments.com/hc/en-us/articles/210275605-How-Can-I-Optimize-the-Performance-of-KONTAKT-5-