See: https://github.com/mozilla/build-cloud-tools/pull/202 and https://bugzilla.mozilla.org/show_bug.cgi?id=1257215

test-mount.ps1

function Write-Log {
  <#
  .Synopsis
    Logs to the userdata run log file, with timestamps.
  .Parameter message
    The body of the log message
  .Parameter severity
    The severity of the message, to enable filtering in log aggregators or reporting.
  .Parameter path
    The full path to the log file.
  #>
  param (
    [string] $message,
    [string] $severity = 'INFO',
    [string] $path = ('{0}\log\userdata-run.log' -f $env:SystemDrive)
  )
  if (!(Test-Path $path)) {
    [Environment]::SetEnvironmentVariable('OutputToConsole', 'true', 'Process')
  }
  $formattedMessage = ('{0} [{1}] {2}' -f [DateTime]::Now.ToString("yyyy-MM-dd HH:mm:ss zzz"), $severity, $message)
  Add-Content -Path $path -Value $formattedMessage
  switch ($severity) 
  {
    #{Error | Warning | Information | SuccessAudit | FailureAudit}
    'DEBUG' {
      $foregroundColor = 'DarkGray'
      $entryType = 'SuccessAudit'
      $eventId = 2
      break
    }
    'WARN' {
      $foregroundColor = 'Yellow'
      $entryType = 'Warning'
      $eventId = 3
      break
    }
    'ERROR' {
      $foregroundColor = 'Red'
      $entryType = 'Error'
      $eventId = 4
      break
    }
    default {
      $foregroundColor = 'White'
      $entryType = 'Information'
      $eventId = 1
      break
    }
  }
  if ($env:OutputToConsole -eq 'true') {
    Write-Host -Object $formattedMessage -ForegroundColor $foregroundColor
  }
  $logName = 'Application'
  $source = 'Userdata'
  if (!([Diagnostics.EventLog]::Exists($logName)) -or !([Diagnostics.EventLog]::SourceExists($source))) {
    New-EventLog -LogName $logName -Source $source
  }
  Write-EventLog -LogName $logName -Source $source -EntryType $entryType -Category 0 -EventID $eventId -Message $message
}
function Prep-Spot {
  param (
    [switch] $force
  )
  begin {
    Write-Log -message ("{0} :: Function started" -f $($MyInvocation.MyCommand.Name)) -severity 'DEBUG'
  }
  process {
    if (!$force -and (Get-EventLog -logName 'Application' -source 'Userdata' -message 'Prep-Spot :: Function ended' -newest 1 -ErrorAction SilentlyContinue)) {
      Write-Log -message ("{0} :: detected prior run. skipping spot setup" -f $($MyInvocation.MyCommand.Name)) -severity 'DEBUG'
    } else {
      $mountPath = ('{0}\mnt' -f $env:SystemDrive) # if this folder exists and is empty and a Z: drive exists, mount the Z: drive to the folder.
      if ((Test-Path -Path $mountPath -PathType Container -ErrorAction SilentlyContinue) -and ((Get-ChildItem $mountPath | Measure-Object).Count -eq 0)) {
        Mount-EphemeralDisks -path $mountPath
      }
    }
  }
  end {
    Write-Log -message ("{0} :: Function ended" -f $($MyInvocation.MyCommand.Name)) -severity 'DEBUG'
  }
}

# this function will not work on instances that have more than one, non-ephemeral disk (eg: c:, d: where both are gp2 or iops).
# it will likely do nasty things if that is the case.
function Mount-EphemeralDisks {
  param (
    [string] $path = ('{0}\mnt' -f $env.SystemDrive)
  )
  begin {
    Write-Log -message ("{0} :: Function started" -f $($MyInvocation.MyCommand.Name)) -severity 'DEBUG'
  }
  process {
    $outfile = ('{0}\log\{1}.diskpart.stdout.log' -f $env:SystemDrive, [DateTime]::Now.ToString("yyyyMMddHHmmss"))
    $errfile = ('{0}\log\{1}.diskpart.stderr.log' -f $env:SystemDrive, [DateTime]::Now.ToString("yyyyMMddHHmmss"))
    $ephemeralVolumeCount = @(Get-WmiObject Win32_Volume | ? { ($_.DriveLetter -and !($_.SystemVolume) -and (-not ($_.DriveLetter -ieq $env:SystemDrive))) }).length
    $volumeOffset = ($ephemeralVolumeCount - (@(Get-WmiObject Win32_Volume).length)
    $diskpartscript = @(
      '',
      "select volume 1`nremove all dismount`nselect disk 1`nclean`nconvert gpt`ncreate partition primary`nformat quick fs=ntfs`nselect volume 1`nassign mount=C:\mnt",
      "select disk 1`nclean`nconvert dynamic`nselect disk 2`n clean`nconvert dynamic`ncreate volume stripe disk=1,2`nselect volume $volumeOffset`nformat quick fs=ntfs`nassign mount=C:\mnt"
    )
    if (($ephemeralVolumeCount -gt 0) -and ($volumeOffset -gt 0) -and ($ephemeralVolumeCount -lt $diskpartscript.length)) {
      New-Item -path ('{0}\mnt.dp' -f $env:Temp) -value $diskpartscript[$ephemeralVolumeCount] -itemType file -force
      Start-Process 'diskpart' -ArgumentList @('/s', ('{0}\mnt.dp' -f $env:Temp)) -Wait -NoNewWindow -PassThru -RedirectStandardOutput $outfile -RedirectStandardError $errfile
      if (-not ((Get-Item $errfile).length -gt 0kb)) {
        Write-Log -message ('{0} :: ephemeral volume(s) mounted at {1}. {2}' -f $($MyInvocation.MyCommand.Name), $path, (Get-Content $outfile)) -severity 'INFO'
      } else {
        Write-Log -message ("{0} :: failed to mount ephemeral volume(s) at {1}. {2}" -f $($MyInvocation.MyCommand.Name), $path, (Get-Content $errfile)) -severity 'ERROR'
      }
    } else {
      Write-Log -message ('{0} :: mount skipped. volume count was: {1}' -f $($MyInvocation.MyCommand.Name), $ephemeralVolumeCount) -severity 'DEBUG'
    }
  }
  end {
    Write-Log -message ("{0} :: Function ended" -f $($MyInvocation.MyCommand.Name)) -severity 'DEBUG'
  }
}
Prep-Spot #-force