It takes me around 3 mins to render out 6 seconds of that. Does that seem reasonable?
Yes, that is a short render time.
Sometimes,depending on effects and other items used, each frame may take minutes to render.
> Also, I noticed that Multiprocessing only seems to work for the first 50 frames or so, then it just switches out to rendering 1 frame at a time. Any idea why this might be?
You haven't preserved enough RAM for use by processes other than the background rendering processes. When the foreground RAM cache fills up (or when another application on your system wants RAM), the background processes need to stop rendering and return the RAM for use by these other processes.
See this page for information about memory and improving performance in After Effects: http://adobe.ly/dC0MdR
Thanks Todd, This pretty much confirms my own research
The only thing im still a bit mistified on is the amount of ram i should be reserving. From my somewhat basic understanding of how a computer works i thought i had dedicated plenty! I did 7 different configerations and the bellow image is the one that rendered quickest for me. However it still seemed to stop multiprocessing after the first 50 frames. Am looking at upgrading the RAM to 128Gb
Any suggestions on this current configuration?
For starters, try using fewer CPUs (reserve more CPUs for other applications). Follow the link that I gave above and read the article that it refers to about not overscheduling your processors.
Also, the rule of thumb is to start by reserving 1/3-1/4 of your installed RAM for other processes.
This is just my own personal experience, so certainly listen to Todd more than me... but try to reserve 1/2 or more of your available hyperthreaded cores for other apps and see if that helps.
Keep your available AE CPUs equal to or less than the number of real physical CPU cores you have (in your case 16 or less). Also, AE seems to handle multiprocessing better after a fresh machine reboot. (YMMV)
Are you rendering to an SSD? Is your Global Performance Cache on an SSD? Having 30 instances of any app reading and writing to the same HDD is going to be a strain on your I/O bandwidth.