@JBinFla, assuming you are on linux; read up on tmpfs
.
That basically creates a file system in RAM which you can mount and use as scratch space for Duplicati tempdir.
For example you can create this in /etc/fstab:
# <file system> <mount point> <type> <options> <dump> <pass>
duplicati_tmp /mnt/duplicati_tmp tmpfs defaults,size=32G 0 0
I have not used duplicati for a while so I do not know if there are any other cache items to take care of. This thread touches on that:
hth.