Powershell

Create big fake uncompressible files (and this is for a good reason)

Grégory Laroche

Grégory Laroche

— 2 min read
Create big fake uncompressible files (and this is for a good reason)
Photo by Victor Freitas / Unsplash

Sometimes, for backup performance tests or disaster recovery drills, I need a server that can take a real beating. Not your usual 40GB VM—nope, I’m talking a heavyweight 500GB to 1TB beast.

But here’s the kicker: my lab isn’t at home...
So, to load a VM, I have to send all that data through my WAN. 😥

But then, a tiny elf in my head suddenly chimes in and says "hey buddy, why not let the VM create the file itself ? And for a challenge, make it uncompressible !"

Snap ! here we go !

Let's build a PowerShell script that can create those files to fill-up this server.

# Define the path and number of files
$filePath = "C:\files" # Change this to your desired path
$numberOfFiles = 100 # Change this to the number of files you want to create

# Function to create a file with random data
function CreateRandomFile([string]$fileName, [int]$sizeInBytes) {
    $fileStream = [System.IO.File]::Create($fileName)
    $random = New-Object System.Random
    $buffer = New-Object byte[] 10MB
    $totalBytesWritten = 0

    while ($totalBytesWritten -lt $sizeInBytes) {
        $random.NextBytes($buffer)
        $bytesToWrite = [Math]::Min($buffer.Length, $sizeInBytes - $totalBytesWritten)
        $fileStream.Write($buffer, 0, $bytesToWrite)
        $totalBytesWritten += $bytesToWrite
    }

    $fileStream.Close()
}

# Create the files
for ($i = 1; $i -le $numberOfFiles; $i++) {
    $fileName = Join-Path $filePath ("RandomFile$i.bin")
    CreateRandomFile $fileName 1073741824 # 1 GB
}

This script will create X number of files with Y of size in the Z folder.
Where X, Y and Z are variable to change in the script.

You should see new files created to your path directory :

But wait, are these files compressible ? Will the backup process shrink them before sending them off to the backup destination ?
Let's try to Zip them.

Et voila ! 0% compression rate !
(It is actually heavier than the originals thanks to the Zip headers).
👍

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