Hyper-V Host Memory Utilization with PowerShell

Posted on September 24, 2015 by Jeff Hicks in Hyper-V, PowerShell with

Several weeks ago, I posted a PowerShell script on my blog that uses commands in the Hyper-V module to report on memory utilization per virtual machine. I rely heavily on virtualization to provide a complete domain environment since I work at home. At present, my workload is spread between laptop running 8GB of RAM and a Gigabyte Brix with 16GB of RAM. I’m in the process of planning for something new. But in the meantime, memory utilization, especially from the Hyper-V host perspective is important to me. So I thought I’d share with you some PowerShell-related suggestions that should give you a good idea of how much memory is being used and what virtual machine is using it.

I’m going to be querying my Hyper-V server from my desktop.

$Computername = "chi-hvr2"

The first step I can take is to query WMI for the Win32_OperatingSystem. I’m using Get-CimInstance as I am trying to wean myself off of Get-WmiObject.

get-ciminstance -ClassName Win32_OperatingSystem -ComputerName $computername | 
Select PSComputername,Free*Memory,Total*MemorySize

I’ve selected a few memory related properties.

Memory properties from the Win32_OperatingSystem class (Image Credit: Jeff Hicks)

Memory properties from the Win32_OperatingSystem class (Image Credit: Jeff Hicks)

The memory values are in KB. If I divide the number by 1KB that will give me the value in MB. If I divide by 1MB, I’ll get the value in GB. Here’s a more complete one-line command that also calculates utilization percentages.

Get-CimInstance -ClassName Win32_OperatingSystem -ComputerName $computername |
Select PSComputername,
@{Name="OS";Expression = {$_.Caption}},
@{Name = "TotalMemoryGB";Expression={$_.totalVisibleMemorySize/1MB -as [int]}},
@{Name = "FreeMemoryGB";Expression={[Math]::Round($_.FreePhysicalMemory/1MB,2)}},
@{Name = "PctMemoryFree";Expression = {[Math]::Round(($_.FreePhysicalMemory/$_.totalVisibleMemorySize) *100,2)}},
@{Name = "TotalVirtualMemoryGB";Expression={$_.totalVirtualMemorySize/1MB -as [int]}},
@{Name = "FreeVirtualMemoryGB";Expression={[Math]::Round($_.FreeVirtualMemory/1MB,2)}},
@{Name = "PctVirtualMemoryFree";Expression = {[Math]::Round(($_.FreeVirtualMemory/$_.totalVirtualMemorySize) *100,2)}}
A formatted display of memory properties (Image Credit: Jeff Hicks)

A formatted display of memory properties (Image Credit: Jeff Hicks)

As you can see, memory is getting pretty tight. What virtual machines are eating this memory up? To figure that out, I need to get all the currently running VMs.

$vms = Get-VM -ComputerName $computername | where {$_.state -eq 'running'}

How much memory is currently assigned?

$stat = $vms | measure memoryassigned –sum
$stat.sum/1GB
Total assigned virtual machine memory (Image Credit: Jeff Hicks)

Total assigned virtual machine memory (Image Credit: Jeff Hicks)

But probably more important is how much memory is actually being demanded?

Total virtual machine memory demanded (Image Credit: Jeff Hicks)

Total virtual machine memory demanded (Image Credit: Jeff Hicks)

There is also a maximum memory, which would be a worst case scenario. Here’s a one-line approach to getting the value.

($vms | measure MemoryMaximum -sum).sum/1GB
Potential maximum VM memory (Image Credit: Jeff Hicks)

Potential maximum VM memory (Image Credit: Jeff Hicks)

If all the current running VMs needed to use their maximum memory settings, they would need 23GB. That’s a problem because the server only has 16! Hopefully it won’t come to that. With this, I can create a custom object to display total virtual machine memory utilization.

[pscustomobject]@{
Computername = $Computername.toUpper()
RunningVMs = $vms.count
TotalAssignedMemoryGB = ($vms | Measure-Object -Property MemoryAssigned -sum).sum/1GB
TotalDemandMemoryGB = ($vms | measure-object -Property MemoryDemand -sum).sum/1GB
PctDemand = [math]::Round(($vms.memorydemand | measure-object -sum).sum/($vms.memoryassigned | measure-object -sum).sum * 100,2)
TotalMaximumMemoryGB = ($vms | Measure-Object -Property MemoryMaximum -sum).sum/1GB
}
A VM memory summary (Image Credit: Jeff Hicks)

A VM memory summary (Image Credit: Jeff Hicks)

Notice I’m not simply writing text to the screen I am using an object. This makes it much easier if I had multiple hosts to manage, or if I wanted to export to a CSV or something.

I can take this a step further and look at each running VM. Since I can get each machine’s assigned and demand memory, I can divide those values by the host’s available memory and calculate what percentage each VM is consuming.

$vmhost = Get-CimInstance -ClassName Win32_OperatingSystem -ComputerName $computername
$usage = $vms | select Name,
@{Name="Status";Expression={$_.MemoryStatus}},
@{Name="MemAssignMB";Expression={$_.MemoryAssigned/1MB}},
@{Name="PctAssignTotal";Expression={[math]::Round(($_.memoryAssigned/($vmhost.TotalVisibleMemorySize*1KB))*100,2)}},
@{Name="MemDemandMB";Expression={$_.MemoryDemand/1MB}},
@{Name="PctDemandTotal";Expression={[math]::Round(($_.memoryDemand/($vmhost.TotalVisibleMemorySize*1KB))*100,2)}}

I saved the results to a variable, so I could do different things with it like this:

$usage | sort PctDemandTotal -Descending | format-table
VM utilization of host memory (Image Credit: Jeff Hicks)

VM utilization of host memory (Image Credit: Jeff Hicks)

Looks like my SQL Server needs some attention, or I could shut a few things down to free up resources.

In any event, I’ve given you several commands you could run to get a handle on memory utilization on the Hyper-V host. But personally, I’d prefer everything in one place. So I wrote a function that combines everything I’ve covered.

#requires -version 4.0
#requires -module Hyper-V

Function Get-VMHostMemoryStatus {
<#
.Synopsis
Get a memory summary for a Hyper-V host
.Description
This command will get a summary of memory utilization for a Hyper-V host. Unless otherwise indicated, memory sizes are in GB. 
The VMs property will be a nested collection of running virtual machines showing what percentage of total host physical memory each virtual machine is assigned and demanding. See examples.
.Parameter Computername
The name of a Hyper-V host. This parameter has an alias of CN.
.Example
PS C:\> Get-VMHostMemoryStatus chi-hvr2 -outvariable h


Computername         : CHI-HVR2
OperatingSystem      : Microsoft Hyper-V Server 2012 R2
TotalMemory          : 16
FreeMemory           : 2.05
PctMemoryFree        : 12.91
TotalVirtualMemory   : 18
FreeVirtualMemory    : 4.35
PctVirtualMemoryFree : 23.8
RunningVMs           : 7
TotalAssignedMemory  : 12.845703125
TotalDemandMemory    : 8.9794921875
PctDemand            : 69.9
TotalMaximumMemory   : 23
VMs                  : {@{Name=CHI-CORE01; Status=Low; MemAssignMB=513; PctAssignTotal=3.15; MemDemandMB=492; PctDemandTotal=3.03}, 
                       @{Name=CHI-DC04; Status=OK; MemAssignMB=2049; PctAssignTotal=12.6; MemDemandMB=799; PctDemandTotal=4.91}, 
                       @{Name=CHI-FP02; Status=Warning; MemAssignMB=821; PctAssignTotal=5.05; MemDemandMB=845; PctDemandTotal=5.2}, 
                       @{Name=CHI-SCOM01; Status=OK; MemAssignMB=4096; PctAssignTotal=25.19; MemDemandMB=1720; 
                       PctDemandTotal=10.58}...}
.Example
PS C:\> $h.vms | Sort PctDemandTotal -descending | format-table

Name       Status  MemAssignMB PctAssignTotal MemDemandMB PctDemandTotal
----       ------  ----------- -------------- ----------- --------------
CHI-SQL01  Warning        2653          16.32        2732           16.8
CHI-Win81  Low            2050          12.61        1927          11.85
CHI-SCOM01 OK             4096          25.19        1679          10.33
CHI-FP02   Warning         777           4.78         808           4.97
CHI-DC04   OK             2049           12.6         799           4.91
CHI-Web02  OK             1024            6.3         655           4.03
CHI-CORE01 Low             513           3.15         492           3.03

The running virtual machines and how much memory each is using.

.Notes
Version 1.0

Learn more about PowerShell:
Essential PowerShell Resources
**************************************************************** * DO NOT USE IN A PRODUCTION ENVIRONMENT UNTIL YOU HAVE TESTED * * THOROUGHLY IN A LAB ENVIRONMENT. USE AT YOUR OWN RISK. IF * * YOU DO NOT UNDERSTAND WHAT THIS SCRIPT DOES OR HOW IT WORKS, * * DO NOT USE IT OUTSIDE OF A SECURE, TEST SETTING. * **************************************************************** .Link Get-VM Get-VMHost Get-CimInstance #> [cmdletbinding()] Param( [Parameter(Position=0,Mandatory,HelpMessage="Enter the name of a Hyper-V host")] [Alias("cn")] [ValidateNotNullorEmpty()] [string]$Computername ) Write-Verbose "[Starting] $($MyInvocation.Mycommand)" Try { Write-Verbose "[Status] Getting Operating system information from $Computername" $vmhost = Get-CimInstance -computername $Computername -ClassName Win32_OperatingSystem -ErrorAction Stop Write-Verbose "[Status] Getting running virtual machines" $vms = Get-VM -Computername $Computername -ErrorAction Stop | where {$_.state -eq 'running'} } Catch { Throw $_ #bail out Return } Write-Verbose "[Status] Analyzing..." $vmusage = $vms | select Name, @{Name = "Status";Expression={$_.MemoryStatus}}, @{Name = "MemAssignMB";Expression={$_.MemoryAssigned/1MB}}, @{Name = "PctAssignTotal";Expression={[math]::Round(($_.memoryAssigned/($vmhost.TotalVisibleMemorySize*1KB))*100,2)}}, @{Name = "MemDemandMB";Expression={$_.MemoryDemand/1MB}}, @{Name = "PctDemandTotal";Expression={[math]::Round(($_.memoryDemand/($vmhost.TotalVisibleMemorySize*1KB))*100,2)}} [pscustomobject]@{ Computername = $vmhost.CSName OperatingSystem = $vmhost.Caption TotalMemory = $vmhost.totalVisibleMemorySize/1MB -as [int] FreeMemory = [Math]::Round($vmhost.FreePhysicalMemory/1MB,2) PctMemoryFree = [Math]::Round(($vmhost.FreePhysicalMemory/$vmhost.totalVisibleMemorySize) *100,2) TotalVirtualMemory = $vmhost.totalVirtualMemorySize/1MB -as [int] FreeVirtualMemory = [Math]::Round($vmhost.FreeVirtualMemory/1MB,2) PctVirtualMemoryFree = [Math]::Round(($vmhost.FreeVirtualMemory/$vmhost.totalVirtualMemorySize) *100,2) RunningVMs = $vms.count TotalAssignedMemory = ($vms | Measure-Object -Property MemoryAssigned -sum).sum/1GB TotalDemandMemory = ($vms | measure-object -Property MemoryDemand -sum).sum/1GB PctDemand = [math]::Round(($vms.memorydemand | measure-object -sum).sum/($vms.memoryassigned | measure-object -sum).sum * 100,2) TotalMaximumMemory = ($vms | Measure-Object -Property MemoryMaximum -sum).sum/1GB VMs = $vmusage } Write-Verbose "[Ending] $($MyInvocation.Mycommand)" } #end function

Now, I can get everything I need with a single command.

Get-VMHostMemoryStatus -Computername chi-hvr2 -OutVariable hv
Getting Hyper-V host memory status (Image Credit: Jeff Hicks)

Getting Hyper-V host memory status (Image Credit: Jeff Hicks)

I modified the property names, as I thought they were getting a bit long for my tastes. The memory values are in GB. Details for each running virtual machine are stored in the VMs property. Because I used the common parameter Out-Variable, I can easily get that information without having to re-run the command.

Viewing VM memory details (Image Credit: Jeff Hicks)

Viewing VM memory details (Image Credit: Jeff Hicks)

Because everything is an object I can slice and dice the data anyway, I need or use any other PowerShell cmdlet. I hope you’ll let me know what you think. Now if you’ll excuse me, I think I have some virtual machines that need some attention.

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