Which Hyper-V VM Worker Process Belongs To Which VM?

Warning! This info is not totally accurate! Please read the next day's post for corrections.

I wanted to track down which virtual machine on my Hyper-V host was causing an inordinate amount of disk I/O on my host without logging in to each one.

In Hyper-V, you will notice that on the root partition, you will see one instance of vmms.exe (VM Management Service,) and then you will see a separate instance of vmwp.exe (VM Worker Process) for each virtual machine that is currently running.

Notice that the vmwp.exe processes run under a special user context which contains the GUID that you would find in that virtual machine's configuration files on disk. The same GUID is also supplied to vmwp.exe as an argument as the process is created, like so:

"C:\Windows\System32\vmwp.exe" c83cdee4-1a6d-4f51-9d05-e57df8403ed4

It's not immediately apparent which vmwp.exe belongs to which VM. Furthermore, the I/O charged against each individual vmwp.exe process is not necessarily indicative of what's actually happening on the virtual machine that its hosting. So we'll need to go to the performance counters instead. The "Hyper-V Virtual IDE Controller (Emulated)" set of counters should do the trick, assuming you're using the IDE controller on your VMs.

I have all the information I need now to determine which virtual machine is responsible for the large amount of I/O... but I didn't want to just do it manually. Why not write a reusable tool that can also be run on Core servers with no GUI?

So this simple script, when run on a Hyper-V host, does just that. The output looks like this:

Get-VMPidAndIO | Out-GridView

My VMs were all idle then, hence all the zeros. The screenshot loses all its dramatic flair, but whatever.

The script could easily be enhanced by supporting remote Hyper-V hosts, alternate credentials, etc. But what do you want for 30 minutes?

#Requires -Version 3
function Get-VMPidAndIO
{
<#
.SYNOPSIS
	Gets the Process ID and I/O statistics of each virtual machine running on the Hyper-V host.
.DESCRIPTION
	Gets the Process ID and I/O statistics of each virtual machine running on the Hyper-V host.
    Currently only works for VMs using virtual IDE controllers.
    Requires Powershell 3 at a minimum.
.LINK
    http://myotherpcisacloud.com
.NOTES
    Written by Ryan Ries, June 2013.
    ryan@myotherpcisacloud.com
#>
    BEGIN
    {
        Try
        {
            $VMProcesses = Get-CimInstance -Query "Select ProcessId,CommandLine From Win32_Process Where Name ='vmwp.exe'" -ErrorAction Stop
        }
        Catch
        {
            Write-Error $_.Exception.Message
            Return
        }
    }
    PROCESS
    {

    }
    END
    {
        Foreach($_ In $VMProcesses) 
        {
            $VMName = $((Get-VM | Where Id -EQ $_.CommandLine.Split(' ')[-1]).Name)            
            [PSCustomObject]@{PID=$_.ProcessId;
                              VMName=$VMName; 
                              ReadBytesPerSec=[Math]::Round($(Get-Counter "\Hyper-V Virtual IDE Controller (Emulated)($VMName`:Ide Controller)\Read Bytes/sec").CounterSamples.CookedValue, 2);
                              WriteBytesPerSec=[Math]::Round($(Get-Counter "\Hyper-V Virtual IDE Controller (Emulated)($VMName`:Ide Controller)\Write Bytes/sec").CounterSamples.CookedValue, 2); }
        }

    }
}

Comments (1) -

ANy chance of making a script that is compatible with Hyper-V Server 2008R2?

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