Assign a mount point folder path to a drive using PowerShell
The Commandlet that I needed was Add-PartitionAccessPath
I set things up the way I wanted through the GUI on disk 2, created a partion on Disk 3 and then carefully compared the properties. The key was here:
(Get-Partition -DiskNumber 2).AccessPaths
(Get-Partition -DiskNumber 3).AccessPaths
There was an additional AccessPath for Disk2, which led me across a number of MSDN articles looking for a method, until I finally found that there already is a command for it.
The following command sealed the deal:
$Partition | Add-PartitionAccessPath -AccessPath "G:\Folder01"
For reference, here's the full solution:
$Disk = Get-Disk 3
# $Disk | Clear-Disk -RemoveData -Confirm:$false
$Disk | Initialize-Disk -PartitionStyle MBR
$disk | New-Partition -UseMaximumSize -MbrType IFS
$Partition = Get-Partition -DiskNumber $Disk.Number
$Partition | Format-Volume -FileSystem NTFS -Confirm:$false
New-Item -ItemType Directory -Path "G:\Folder01"
$Partition | Add-PartitionAccessPath -AccessPath "G:\Folder01"
How to assign a drive to a NTFS Folder in Powershell using Command Line:
cmd /c 'subst G: "C:\Folder1"'
Note: Explorer is showing the same size of the folder as the C:.