How to cache (more) data on SSD/RAM to avoid spin up?

Question

I have Ubuntu server 12.04 running on a 40GB SSD with a raid 5 mounted for media files. I access the files often via samba either with a Raspberry Pi for music playback or with another PC for the other files.
I want to avoid the spin up of the raid by caching often used data.
This is already happening, when for exmaple I play back the same music folder after spin down. But it seems to only cache the last request I did.

Is there a way to make the cache larger/more intelligent?
For example I ALWAYS want to have the root file structure of the raid cached.
At the moment it appears only the last request before spin down is cached.

It would also be awesome to cache the whole file structure so spin up is only needed when I actually access a file.

tl;dr Is there a way to permantly cache something? (or something similar)

Answer 1

you can use BCache on Linux to enable caching of the file drive by using your SSD as a cache. That should probably alleviate any need to spin up the disks for read operations. Just shrink your existing os partition and set aside a few gigs for use as a cache.