Resolved cMP 2008 + 64GB MEM = SLOW DISKS while 48 GB = FAST DISKS; why?

[alexffff]

Thanks for sharing your take on this, JimJ.. I carried out both tests with varying results on 10.8 vs 10.9/.10/.11

I'm suspecting the introduction of the memory compression feature in 10.9 onwards as I was able to utilize the full 64gb of ram in 10.8 with no negative impact whatsoever on the overall performance of the mac, including SSD performance ~480MB/s write and ~510MB/s read. As soon as I dropped the ram capacity to 48 or 56GB, the performance was stellar (for the 3,1) on 10.9+

I also tried disabling the memory compression + swap using vm_compressor=1 on 10.9+ but it was causing kernel panics / crashes.



Thanks for confirming the performance anomaly... 56GB is the sweet spot for the mac pro 2008 with vm_compressor=2 set in nvram (swap disabled). Everything is so zappy ie. virtual machines (startup/shutdown,copying, compiling), startup/shutdown times, copying and opening files.. can't believe I've been running the mac with 64gb for the past 8 months with such sluggish performance.

By the way - if you wish to utilize the maximum memory performance using 56GB (6x 8GB and 2x 4GB) in the 3,1, install the 2x 4GB modules in memory slots A3/A4 on Riser A as Riser B should be maxed out with the 8GB sticks due to the fact that it is assigned branch 0 in the north bridge memory controller and Riser A is assigned branch 1 - see attached diagram and screenshot of system information/memory.

Results: 11000+ MB/s fill rates and 6000+ MB/s copy rates which I wasn't able to achieve with any other combination amounting to 56GB.

View attachment 605268 View attachment 605269

Hi W1SS,
I have followed your instructions for installing 56GB of Ram in my MacPro 3,1 and everything is working. Thanks!

You mention the "vm_compressor=2 set in nvram (swap disabled)". Is this a requirement and if so how do I go about activating it. I'm guessing through the Terminal but I don't know how to go about it. Any help would be greatly appreciated.
This is where I'm at now.
View attachment 608794

I can only confirm that there is evidence and wide consensus - as far as the MP is a 4- or 8-core type are concerned like with your MP) . 12-cores seem to work fine with all 8 slots full of RAM, 6-cores with 4 full slots.

If I recall correctly, even the position of the empty slots is important, not only to have two of them free of RAM. And - again: If I recall correctly - for the first MP it is different from 4,1/5,1 MP (different architecture)

But you should be capable to do the test yourself: Change the positions and run each time a performance-test.

(Ok, I know this will result in a LOT of tests… but with a little chance….)

Hi guys!

Please check my solution how to run MP3,1 with 56 or 62Gb RAM available without speed penalty (with 64Gb installed)
https://forums.macrumors.com/threads/mac-pro-3-1-nvme-support-upgrade-guide-questions.2194878/

See Max RAM in MP3,1. 62, 56 or 64Gb [Partially SOLVED] and Can I have more RAM? Yes, you can run 62Gb!