Can't use all memory for VM

Question

Hi!
I have Microsoft Hyper-V Server 2012 R2 with 16 Gb RAM. I created two VM with 7162 Mb of fixed memory on each. But i can't start both of them. When i tried start second vm i got out of memory error. Why?
PS C:\Users\Administrator> ( Get-WMIObject Win32_OperatingSystem -ComputerName localhost ).FreePhysicalMemory
8184452
PS C:\Users\Administrator> start-vm oldBSD
start-vm : 'oldBSD' could not initialize. (Virtual machine ID 05EA5A45-601F-4CC0-8770-62B97571D8F8)
Not enough memory in the system to start the virtual machine oldBSD with ram
size 7168 megabytes. (Virtual machine ID 05EA5A45-601F-4CC0-8770-62B97571D8F8)
The server ran out of available memory.
Max memory value for second machine is 5740Mb, but with it i have
PS C:\Users\Administrator> ( Get-WMIObject Win32_OperatingSystem -ComputerName
localhost ).FreePhysicalMemory
2243312
How i can use all memory? My idea is use 7 Gb of memory for each machine and 1.5-2 Gb for host.

Answer 1

Hi maxx-ode,
As far as I know ,to get free memory you still need to subtract the "standby memroy" from the output of the command in your original post .
Please refer to the article "Memory Sizing Guidance for Windows 7" within the link below :
http://msdn.microsoft.com/en-US/library/windows/hardware/dn550976
" Standby List
The Standby list contains unmodified pages that have been removed from process working sets, which effectively makes the Standby list a cache. If a process needs a page that is on the Standby list, the memory manager immediately returns the page to its
working set.
All pages on the Standby list are available for memory allocation requests. If a process requests memory, the memory manager can take a page from the Standby list, initialize it, and allocate it to the calling process. This is called repurposing a page.
Pages on the Standby list are often from recently used files. By keeping these pages on the Standby list, the memory manager reduces the need to read information from the disk. Disk reads
can decrease system responsiveness. "
Please try to use this command to get the "real" free memory of host (in bytes):
(Get-WmiObject Win32_PerfFormattedData_PerfOS_Memory -ComputerName localhost).FreeAndZeroPageListBytes
"Free & Zero Page List Bytes is the amount of physical memory, in bytes, that is assigned to the free and zero page lists. This memory does not contain cached data. It is immediately available for allocation to a process or for system use.
Update: Actually we can allocate some standby RAM to VM , based on my test I can't allocate whole standby RAM .Then I used
RAMMap to check the usage and I found that Mapped file occupied most RAM .For mapped file please refer to following link:
http://blogs.msdn.com/b/khen1234/archive/2006/01/30/519483.aspx
Best Regards
Elton Ji
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