Test Hyper-V VHD Folders with PowerShell

I've recently added a USB 3.0 Express Card adapter to my laptop to provide USB 3.0 functionality. The added performance is very useful in my Hyper-V setup. However, I am running into a glitch that I have yet to figure out where the external drives (the Express card has 2 ports) are still attached and recognized, but the file system is wonky. I can see most of the folders, and files but not really. This is a problem when I fire up a Hyper-V virtual machine with a VHD in one of these folders. Even though I can run a DIR command and see the file, it really isn't there. So I threw together a little function to add to my Hyper-V workflow module to validate folders with VHD and VHDX files.

My virtual machines are spread out among a number of drives. I don't necessarily need to validate every VHD file, but I would like to know that the paths exist. Now, I could simply pass my list of paths to Test-Path.

PS C:\> "G:\VHDs","F:\VHD","D:\VHD","C:\Users\Public\Documents\Hyper-V\Virtual Hard Disks" | Test-Path
True
True
True
True

But my little glitch can lead to a false positive. So I need to take an extra step and validate one of the VHD/VHDX files using the Test-VHD cmdlet. Here's my function.

#requires -version 3.0

Function Test-VHDPath {

[cmdletbinding()]
Param (
[ValidateNotNullorEmpty()]
[ValidateScript({Test-Path $_})]
#paths to my virtual hard disks for Hyper-V virtual machines
[string[]]$paths = @("G:\VHDs","F:\VHD","D:\VHD","C:\Users\Public\Documents\Hyper-V\Virtual Hard Disks")
)

Write-Verbose "Starting $($MyInvocation.mycommand)"

foreach ($path in $paths) {
  Try {
    #grab the first VHD\VHDX file and test it. No guarantee other files are OK
    #but at least I know the path has been verified.
    Write-Verbose "Validating $path"
    dir $path\*.vhd,*.vhdx | Select -first 1 | Test-VHD -ErrorAction Stop | out-null
  }
  Catch {
    Write-Error "Failed to validate VHD\VHDX files in $Path. $_.Exception.Message"
    Return
  }
}

#if no errors were found then return a simple True
Write-Verbose "No problems found with VHD paths"
Write $True

} #end function

The function gets the first VHD or VHDX file in each folder and tests it. If the test fails, Test-VHD throws an exception which I catch and then bail out. Otherwise, if there are no errors, the function writes $True to the pipeline. Otherwise, I'll get an exception.

But now I have a tool to quickly verify paths before I start trying to launch virtual machines.

If you'd like to learn more about Test-VHD, take a look at my article on the Altaro Hyper-V blog. If you want to try out my function, you should be able to toggle to plain code and copy and paste.

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