System improvement on adding a 2nd hard disk

[subhodiproy299569]

Can you please tell me that why using a higher cache hard disk improves system performance ? And also why using a higher cache hard disk reduces system ram usage ?

 

[CountMike]

Caches work in "first in - first out" principle, any data that doesn't fit or cases cache overflow has to be written to disk before any more data could be admitted to cache otherwise would have to stay in RAM until it turn comes. Data comes in blocks 512 or 1024 bits wide and only one bit over cache capacity can cause it to stay in RAM (which is slower) and may have to wait several turns to be written to cache and than to disk.
Obviously, larger that cache is more data can wait in cache so writes to disk is more even and faster.
Another side effect is different speeds of writing small and large files. With smaller cache, large files start fast but write speed slows down after a while.
Samsung uses some RAM to supplement disk cache for their SSDs and so and so apparently speeds up writes but that works only for continuous, non fragmented data (large files) and doesn't speed 2K files that as most prevalent in OS so it's mostly only visible in benchmarks.