When you are compiling your latest application that will take over the world, it will make a lot a reading and writing against your hard drive. Wouldn’t it be a lot faster if you instead compile against a RAM-drive, and just having your source code on your physical storage devices? To be honest, not much. Despite this disappointment, let us geek out and try it.

Overview

When I am writing this, I assumes that you are using Windows and compiling a .NET or C++ applications. But this solution is very general and should be easy to modify for other conditions.

Symbolic linking

Before we do anything else, it is worth mention symbol linking that has been around in Windows for a long time but is in rarely used. You could use symbolic linking if you want to map a folder into another folder without moving it.

For instance, I have all my repositories in C:\Source\Repos. Recently, when I was working on a large open source project, I run out of disk space. Luckily, I had another hard drive where I could move this project. But I still wanted to navigate to my original path. To solve this, I bring up a command prompt (not PowerShell) and executed:

Command prompt 
C:\Source\Repos>mklink /d TheProject E:\Source\Repos\TheProject
symbolic link created for TheProject <<===>> E:\Source\Repos\TheProject

Now I could find all files in C:\Source\Repos\TheProject even if they were stored on a different drive.

The strategy

When you are working with .NET or C++ applications you could change the directory to be used as output for your compilation. Normally this is bin and obj for .NET, and Debug, Release and x64 for C++. And nothing is stopping you to change these directories in you project file to a RAM-drive. The only problem with this is when you have checked in these changes all your team members will be mad at you because they will get problems with these paths.

So, we will not do this. Instead we will replace all these folders with symbolic links to folders on a RAM drive. This way, no changes are needed to your project and no application will notice any difference. The only exception I have found to this is git that might want to add these new files to the repository. But you could easily avoid this by adding these lines into .gitignore.

Add to .gitignore 
# Symbolic links for .NET applications
[Bb]in
[Oo]bj

# Symbolic links for C++ applications
[Dd]ebug
[Rr]elease
x64

The solution

So, now we just need to find all relevant folders and replace them with symbolic links. Not to fun to manually, so we use PowerShell to solve it. Put this script into a PowerShell file named link-ramdrive.ps1.

PowerShell - link-ramdrive.ps1 
$ramDiskDrive = "R:"

# Find all project files for CSharp, FSharp and Basic
$projectFiles = Get-ChildItem -Include ("*.csproj", "*.fsproj", "*.vbproj") -Recurse 

# Setup directories if any projects found.
if($projectFiles.Length -gt 0)
{
    # Get project directories
    $projectDirectories = $projectFiles | ForEach-Object { $_.DirectoryName } | Get-Unique


    # Create a bin-directory on the RAM-drive
    $projectDirectories | ForEach-Object { New-Item -ItemType Directory -Force -Path "$ramDiskDrive$($_.Substring(2))\bin" } 

    # Remove existing bin-directories
    $projectDirectories | ForEach-Object { Remove-Item "$($_)\bin" -Force -Recurse }

    # Link bin-directories to ramdisk
    $projectDirectories | ForEach-Object { cmd /c mklink /D "$($_)\bin" "$ramDiskDrive$($_.Substring(2))\bin" }


    # Create a obj-directory on the RAM-drive
    $projectDirectories | ForEach-Object { New-Item -ItemType Directory -Force -Path "$ramDiskDrive$($_.Substring(2))\obj" } 

    # Remove existing obj-directories
    $projectDirectories | ForEach-Object { Remove-Item "$($_)\obj" -Force -Recurse }

    # Link obj-directories to ramdisk
    $projectDirectories | ForEach-Object { cmd /c mklink /D "$($_)\obj" "$ramDiskDrive$($_.Substring(2))\obj" }
}


# Find all projects files for C++.
$projectFiles = Get-ChildItem -Include ("*.vcxproj") -Recurse 

# Setup C++-directories is any found.
if($projectFiles.Length -gt 0)
{
    # Get project directories
    $projectDirectories = $projectFiles | ForEach-Object { $_.DirectoryName } | Get-Unique


    $projectDirectories | ForEach-Object { New-Item -ItemType Directory -Force -Path "$ramDiskDrive$($_.Substring(2))\x64" } 

    # Remove existing x64-directories
    $projectDirectories | ForEach-Object { Remove-Item "$($_)\x64" -Force -Recurse }

    # Link x64-directories to ramdisk
    $projectDirectories | ForEach-Object { cmd /c mklink /D "$($_)\x64" "$ramDiskDrive$($_.Substring(2))\x64" }


    $projectDirectories | ForEach-Object { New-Item -ItemType Directory -Force -Path "$ramDiskDrive$($_.Substring(2))\Debug" } 

    # Remove existing Debug-directories
    $projectDirectories | ForEach-Object { Remove-Item "$($_)\Debug" -Force -Recurse }

    # Link Debug-directories to ramdisk
    $projectDirectories | ForEach-Object { cmd /c mklink /D "$($_)\Debug" "$ramDiskDrive$($_.Substring(2))\Debug" }


    $projectDirectories | ForEach-Object { New-Item -ItemType Directory -Force -Path "$ramDiskDrive$($_.Substring(2))\Release" } 

    # Remove existing Release-directories
    $projectDirectories | ForEach-Object { Remove-Item "$($_)\Release" -Force -Recurse }

    # Link Release-directories to ramdisk
    $projectDirectories | ForEach-Object { cmd /c mklink /D "$($_)\Release" "$ramDiskDrive$($_.Substring(2))\Release" }



    # For C++-project, directories in the same folder as the solution file are used for outputs.
    # Find all solution files.
    $projectFiles = Get-ChildItem -Include ("*.sln") -Recurse 

    # Setup C++-directories is any solution file found.
    if($projectFiles.Length -gt 0)
    {
        # Get project directories
        $projectDirectories = $projectFiles | ForEach-Object { $_.DirectoryName } | Get-Unique


        $projectDirectories | ForEach-Object { New-Item -ItemType Directory -Force -Path "$ramDiskDrive$($_.Substring(2))\x64" } 

        # Remove existing x64-directories
        $projectDirectories | ForEach-Object { Remove-Item "$($_)\x64" -Force -Recurse }

        # Link x64-directories to ramdisk
        $projectDirectories | ForEach-Object { cmd /c mklink /D "$($_)\x64" "$ramDiskDrive$($_.Substring(2))\x64" }


        $projectDirectories | ForEach-Object { New-Item -ItemType Directory -Force -Path "$ramDiskDrive$($_.Substring(2))\Debug" }

        # Remove existing Debug-directories
        $projectDirectories | ForEach-Object { Remove-Item "$($_)\Debug" -Force -Recurse }

        # Link Debug-directories to ramdisk
        $projectDirectories | ForEach-Object { cmd /c mklink /D "$($_)\Debug" "$ramDiskDrive$($_.Substring(2))\Debug" }


        $projectDirectories | ForEach-Object { New-Item -ItemType Directory -Force -Path "$ramDiskDrive$($_.Substring(2))\Release" } 

        # Remove existing Release-directories
        $projectDirectories | ForEach-Object { Remove-Item "$($_)\Release" -Force -Recurse }

        # Link Release-directories to ramdisk
        $projectDirectories | ForEach-Object { cmd /c mklink /D "$($_)\Release" "$ramDiskDrive$($_.Substring(2))\Release" }
    }
}

Note that this script assumes you have your RAM-drive named R:.

Also note that this script will remove everything in the folders that will be linked. If that will make you lose something important, you probably are doing something wrong ;-)

We also want to easily undo this. The following script will do that, named that unlink-ramdrive.ps1:

PowerShell - unlink-ramdrive.ps1 
# Find all project files
$projectFiles = Get-ChildItem -Include ("*.csproj", "*.fsproj", "*.vbproj") -Recurse 

# Get project directories
$projectDirectories = $projectFiles | ForEach-Object { $_.DirectoryName } | Get-Unique

# Clear directories if any projects found.
if($projectFiles.Length -gt 0)
{
    # Unlink bin-directories to ramdisk
    $projectDirectories | ForEach-Object { cmd /c rmdir "$($_)\bin"   }

    # Unlink obj-directories to ramdisk
    $projectDirectories | ForEach-Object { cmd /c rmdir "$($_)\obj"   }
}

# Find all projects files for C++.
$projectFiles = Get-ChildItem -Include ("*.vcxproj") -Recurse 

# Setup C++-directories is any found.
if($projectFiles.Length -gt 0)
{
    # Get project directories
    $projectDirectories = $projectFiles | ForEach-Object { $_.DirectoryName } | Get-Unique


    # Unlink x64-directories to ramdisk
    $projectDirectories | ForEach-Object { cmd /c rmdir "$($_)\x64"   }

    # Unlink Debug-directories to ramdisk
    $projectDirectories | ForEach-Object { cmd /c rmdir "$($_)\Debug"   }

    # Unlink Release-directories to ramdisk
    $projectDirectories | ForEach-Object { cmd /c rmdir "$($_)\Release"   }


    # For C++-project, directories in the same folder as the solution file are used for outputs.
    # Find all solution files.
    $projectFiles = Get-ChildItem -Include ("*.sln") -Recurse 

    # Setup C++-directories is any solution file found.
    if($projectFiles.Length -gt 0)
    {
        # Get project directories
        $projectDirectories = $projectFiles | ForEach-Object { $_.DirectoryName } | Get-Unique


        # Unlink x64-directories to ramdisk
        $projectDirectories | ForEach-Object { cmd /c rmdir "$($_)\x64"   }

        # Unlink Debug-directories to ramdisk
        $projectDirectories | ForEach-Object { cmd /c rmdir "$($_)\Debug"   }

        # Unlink Release-directories to ramdisk
        $projectDirectories | ForEach-Object { cmd /c rmdir "$($_)\Release"   }
    }
}

Then all you need to do is to run these scripts to setup your solution in the way you want. Also be aware that when you are restarting your computer, all the symbolic links will be broken because you RAM-drive is empty. To solve this, just run link-ramdrive.ps1 again.

When you are running the scripts you will likely get some warning or errors, but these could safely be ignored.

Performance

So how much time will you save on this? I have been working on a solution where a complete rebuild took 198 seconds with an SSD-drive. When a RAM-drive it went down to 167 seconds. So about 15 % faster if you are lucky. On smaller builds the difference will be less.

Summary

I cannot say that using a RAM-drive will make you save a lot of time. But if you have a lot of RAM it might be worth to try. This solution is easy to both setup and to remove. You will also put a lot less stress on your physical drive.