So, you have 3 hardware boxes with 8G of RAM each, and just one VM with 6GB of RAM allocated on each of the boxes? If this is the case, maybe allocate more memory, not less per VM, 7GB or so and check if this helps to have less frequent crashes.
So, you have 3 hardware boxes with 8G of RAM each, and just one VM with 6GB of RAM allocated on each of the boxes? If this is the case, maybe allocate more memory, not less per VM, 7GB or so and check if this helps to have less frequent crashes.