Vsphere 5.1: Virtual Machine not sharing Host RAM
Hi,
I am using Licensed Vsphere 5.1 (Upgraded from Vsphere 4)
I am facing a problem after upgrade, Virtual machines are not sharing RAM
Like if i have two machine with 2 GB RAM then total RAM Usage on HOST becomes 4 GB but actually active memory usage is about 1 GB only.
This was not a problem in Vsphere 4 it shows active memory as HOST memory usage but in Vsphere 5 Virtual machine are not sharing RAM and reserve full RAM when powered on.
Maybe there is some setting to enable memory sharing or to turn off this full reservation of RAM.
got the answer
Changes are the VMkernel is using large pages to back the virtual memory pages. For more information, this article from Duncan will provide enough information and links to other articles about this topic:
http://www.yellow-bricks.com/2011/01/26/re-large-pages-gabvirtualworld-frankdenneman-forbesguthrie/
In short VMkernel will place the pages issued by the virtual machine in large pages on physical memory to speed up memory access. Large pages are used when the physical CPU that has EPT(Intel) or RVI(AMD) capabilities.