How can I limit the cache used by copying so there is still memory available for other cache?

Question

Basic situation:

I am copying some NTFS disks in openSuSE. Each one is 2TB. When I do this, the system runs slow.

My guesses:

Answer 1

Ok, now that i know that your using rsync and i could dig a bit more:

It seems that rsync is ineffective when used with tons of files at the same time, there's an entry in their FAQ, it's not a linux/cache problem, it's an rsync problem eating too much RAM.

Googling around someone recommended to split the syncing in multiple rsync invocations

Hope it helps.