How to Monitor VM Memory Pressure with PowerShell

In a previous article, I gave you an introduction to using performance counters with Hyper-V and PowerShell. Of course you can use performance counters to manage all sorts of things, but personally, memory is the most critical. Even though I’m running Hyper-V in a non-production setting and don’t have access to massive server farms and back-end storage, the concepts that I am discussing will still apply to those instances. So even though this article is going to look specifically at Dynamic Memory counters, you might need something else. I encourage you, as with all of my content, to look at the techniques and concepts and not focus entirely on the end result.

Finding Instances

I am running Hyper-V on my Windows 10 box and will be querying the local computer. But there’s no reason this won’t work with a remote Hyper-V server. Although I have not tested anything with Window Server 2019. To keep the code re-usable I’ll define a variable for the Hyper-V host. You naturally will set it to whatever you need.

$Computer = $env:COMPUTERNAME

1	$Computer = $env:COMPUTERNAME

I want to check for counter instances on a single virtual machine. In the previous article, I talked about getting counter data from instances so I’m going to use a regular expression pattern to retrieve the instances associated with a given VM.

$VMName = "WIN10"
[regex]$rx = "(?<=\\\\).*(?=\\)"

$c = get-counter -listset 'Hyper-V Dynamic Memory VM' -ComputerName $computer | 
Select -expand PathsWithInstances | where {$_ -match $VMName}

$VMName = "WIN10"

[regex]$rx = "(?<=\\\\).*(?=\\)"

$c = get-counter -listset 'Hyper-V Dynamic Memory VM' -ComputerName $computer |

Select -expand PathsWithInstances | where {$_ -match $VMName}

This is what I get.

Dynamic Memory perfomance counters

I can pass this array of counters to the Get-Counter cmdlet.

Getting counter data

There are a few more but you get the idea.

Monitoring Performance Counters

One of the nice features in Get-Counter is that you can watch a given set of counters. I will trust that you will read full cmdlet help and examples. But I can run this command to collect 10 samples of the specified counters, taking a reading every 2 seconds.

Get-Counter -counter $c -SampleInterval 2 -MaxSamples 10

1	Get-Counter -counter $c -SampleInterval 2 -MaxSamples 10

Don’t get too gung-ho on your sampling interval.

The PowerShell output is far from user-friendly. You might want to save all the output into a variable or export to an XML file. Don’t use CSV. Or, let’s have PowerShell format the results into something a bit more manageable.

Get-Counter -Counter $c | 
Select-object -expandproperty Countersamples |
Sort-object -property InstanceName | 
Select-object -property InstanceName, 
@{Name="Counter";Expression={Split-path $_.path -Leaf}},
Cookedvalue,timestamp,
@{Name="VMHost";Expression={$rx.Match((Split-Path $_.path)).value.ToUpper()}} |
Format-Table

Get-Counter -Counter $c |

Select-object -expandproperty Countersamples |

Sort-object -property InstanceName |

Select-object -property InstanceName,

@{Name="Counter";Expression={Split-path $_.path -Leaf}},

Cookedvalue,timestamp,

@{Name="VMHost";Expression={$rx.Match((Split-Path $_.path)).value.ToUpper()}} |

Format-Table

This is much easier to read.

Formatted performance counters in PowerShell

Or send it to Out-Gridview.

Get-Counter -Counter $c | 
Select-object -expandproperty Countersamples |
Sort-object -property InstanceName | 
Select-object -property InstanceName, 
@{Name="Counter";Expression={Split-path $_.path -Leaf}},
Cookedvalue,timestamp,
@{Name="VMHost";Expression={$rx.Match((Split-Path $_.path)).value.ToUpper()}} |
Out-GridView -Title "Dynamic Memory Counters"

Get-Counter -Counter $c |

Select-object -expandproperty Countersamples |

Sort-object -property InstanceName |

Select-object -property InstanceName,

@{Name="Counter";Expression={Split-path $_.path -Leaf}},

Cookedvalue,timestamp,

@{Name="VMHost";Expression={$rx.Match((Split-Path $_.path)).value.ToUpper()}} |

Out-GridView -Title "Dynamic Memory Counters"

PowerShell performance counters in Out-Gridview

Of course, none of this is actual monitoring. Here’s a code sample that achieves the same result as my earlier snippet: 10 samples at a 2-second interval.

1..10 | foreach {
    $data = Get-Counter -Counter $c | Select-object -expandproperty Countersamples |
    Sort-object -property InstanceName
    clear-Host
    $data | Select-object -property InstanceName, 
    @{Name="Counter";Expression={Split-path $_.path -Leaf}},
    Cookedvalue,timestamp,
    @{Name="VMHost";Expression={$rx.Match((Split-Path $_.path)).value.ToUpper()}} |
    Format-Table
    Start-sleep -Seconds 2
}

1..10 | foreach {

$data = Get-Counter -Counter $c | Select-object -expandproperty Countersamples |

Sort-object -property InstanceName

clear-Host

$data | Select-object -property InstanceName,

@{Name="Counter";Expression={Split-path $_.path -Leaf}},

Cookedvalue,timestamp,

@{Name="VMHost";Expression={$rx.Match((Split-Path $_.path)).value.ToUpper()}} |

Format-Table

Start-sleep -Seconds 2

}

In this example, I am using the PowerShell console window as a monitoring tool. The performance data is written to the console with a refresh every 2 seconds.

Another option is to use my ConvertTo-WPFGrid function which is part of my PSScriptTools module which you can install from the PowerShell Gallery. With this command, I can display the performance counter data in a graphical form that will automatically refresh itself. Here’s a complete code snippet.

$computer = $env:COMPUTERNAME
[regex]$rx = "(?<=\\\\).*(?=\\)"

$VMName = "SRV2"
#get the available counters
$c = get-counter -listset 'Hyper-V Dynamic Memory VM' -ComputerName $computer | 
Select -expand PathsWithInstances | where {$_ -match $VMName} 

1..5 | foreach {
    Get-Counter -Counter $c | Select-object -expandproperty Countersamples |
    Sort-object -property InstanceName | 
    Select-object -property InstanceName, 
    @{Name="Counter";Expression={Split-path $_.path -Leaf}},
    Cookedvalue,TimeStamp,
    @{Name="VMHost";Expression={$rx.Match((Split-Path $_.path)).value.ToUpper()}} |
    ConvertTo-WPFGrid -Title "Dynamic Memory Counters" -Timeout 10 -Height 300 -Width 600 -CenterScreen
}

$computer = $env:COMPUTERNAME

[regex]$rx = "(?<=\\\\).*(?=\\)"

$VMName = "SRV2"

#get the available counters

$c = get-counter -listset 'Hyper-V Dynamic Memory VM' -ComputerName $computer |

Select -expand PathsWithInstances | where {$_ -match $VMName}

1..5 | foreach {

Get-Counter -Counter $c | Select-object -expandproperty Countersamples |

Sort-object -property InstanceName |

Select-object -property InstanceName,

@{Name="Counter";Expression={Split-path $_.path -Leaf}},

Cookedvalue,TimeStamp,

@{Name="VMHost";Expression={$rx.Match((Split-Path $_.path)).value.ToUpper()}} |

ConvertTo-WPFGrid -Title "Dynamic Memory Counters" -Timeout 10 -Height 300 -Width 600 -CenterScreen

}

When run I get something like this:

Display performance counters in a WPF form

My code snippet is getting 5 samples every 10 seconds. You could also use a Do Loop or other techniques to achieve the same effect.

Fine-Tuned Performance Gathering

Before I wrap up for today let me leave you with some techniques for fine-tuning the capture of performance counter data. Let’s say that I am interested in the Pressure counters for a single virtual machine. I can fine tune the regular expression pattern to retrieve just those performance counter instances.

$computer = $env:COMPUTERNAME
$VMName = "SRV2"
[regex]$rx = "(?<=\\\\).*\($VMName\)\\.*Pressure"

#get the available counters
get-counter -listset 'Hyper-V Dynamic Memory VM' -ComputerName $computer | 
Select -expand PathsWithInstances | where {$_ -match $rx}

$computer = $env:COMPUTERNAME

$VMName = "SRV2"

[regex]$rx = "(?<=\\\\).*$$VMName$\\.*Pressure"

#get the available counters

get-counter -listset 'Hyper-V Dynamic Memory VM' -ComputerName $computer |

Select -expand PathsWithInstances | where {$_ -match $rx}

Getting a subset of performance counters

Using this as the foundation and with some additional regular expression voodoo, I can build a little bit of monitoring code for a single virtual machine.

$computer = $env:COMPUTERNAME
$VMName = "SRV2"
[regex]$rx = "(?<=\\\\).*\($VMName\)\\.*Pressure"
[regex]$rxCounter = "(?<=\\\\).*(?=\\)"

#get the available counters
$c = get-counter -listset 'Hyper-V Dynamic Memory VM' -ComputerName $computer | 
Select -expand PathsWithInstances | where {$_ -match $rx} 

for ($i=0;$i -lt 12;$i++) {
    Get-Counter -Counter $c | Select-object -expandproperty Countersamples |
    Sort-Object -property Path |  
    Select-Object -property @{Name="VMHost";Expression={$rxCounter.Match((Split-Path $_.path)).value.ToUpper()}},
    @{Name="VMName";Expression = {$_.InstanceName.toUpper()}}, 
    @{Name="Counter";Expression={Split-Path $_.path -Leaf}},
    Cookedvalue,TimeStamp  |
    ConvertTo-WPFGrid -Title "Memory Pressure for $VMName" -Timeout 5 -Height 180 -Width 530 -CenterScreen
}

$computer = $env:COMPUTERNAME

$VMName = "SRV2"

[regex]$rx = "(?<=\\\\).*$$VMName$\\.*Pressure"

[regex]$rxCounter = "(?<=\\\\).*(?=\\)"

#get the available counters

$c = get-counter -listset 'Hyper-V Dynamic Memory VM' -ComputerName $computer |

Select -expand PathsWithInstances | where {$_ -match $rx}

for ($i=0;$i -lt 12;$i++) {

Get-Counter -Counter $c | Select-object -expandproperty Countersamples |

Sort-Object -property Path |

Select-Object -property @{Name="VMHost";Expression={$rxCounter.Match((Split-Path $_.path)).value.ToUpper()}},

@{Name="VMName";Expression = {$_.InstanceName.toUpper()}},

@{Name="Counter";Expression={Split-Path $_.path -Leaf}},

Cookedvalue,TimeStamp |

ConvertTo-WPFGrid -Title "Memory Pressure for $VMName" -Timeout 5 -Height 180 -Width 530 -CenterScreen

}

Finding the right dimensions takes a little bit of experimentation.

Memory Pressure Performance Data

Next time I’ll wrap up this series on Hyper-V performance counters in PowerShell with a technique I think you’ll find intriguing.

If you’re having problems with your PowerShell scripts use this guide to troubleshoot, diagnose problems and solve your PowerShell woes.

How to Monitor VM Memory Pressure with PowerShell

Finding Instances

Monitoring Performance Counters

Fine-Tuned Performance Gathering

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