Accessing Disk Capacity and Free Space on Remote Computers with PowerShell

Introduction

Managing disk space is a critical task for system administrators, especially when dealing with remote computers. PowerShell offers powerful cmdlets to retrieve disk capacity and free space information remotely. This tutorial will guide you through using PowerShell to access these details efficiently.

Prerequisites

• PowerShell: Ensure you have PowerShell installed on your local machine.
• Remote Access: You need administrative privileges or appropriate permissions to query remote systems.
• PowerShell Remoting: Enable PowerShell remoting on the target computers.

Understanding Key Concepts

Before diving into the commands, it’s essential to understand some key concepts:

• WMI (Windows Management Instrumentation): A core Windows management technology that provides a standardized interface for accessing system information.
• Cmdlets: PowerShell commands designed for specific tasks. Get-WmiObject and Invoke-Command are examples relevant to this tutorial.

Accessing Disk Information Locally

To access disk space on your local machine, you can use the following command:

Get-PSDrive C | Select-Object Used, Free

This cmdlet retrieves information about drive C: and displays its used and free space.

Explanation

• Get-PSDrive: Retrieves information about logical drives.
• Select-Object: Filters the output to show only specified properties (Used, Free).

Accessing Disk Information Remotely

To query a remote computer, PowerShell remoting must be enabled. Here’s how you can do it:

Using WMI with Filtering

You can use Get-WmiObject to access disk information on a remote machine:

$disk = Get-WmiObject Win32_LogicalDisk -ComputerName remotecomputer -Filter "DeviceID='C:'" | Select-Object Size, FreeSpace

To extract and store these values in variables:

$size = (Get-WmiObject Win32_LogicalDisk -ComputerName remotecomputer -Filter "DeviceID='C:'").Size
$freeSpace = (Get-WmiObject Win32_LogicalDisk -ComputerName remotecomputer -Filter "DeviceID='C:'").FreeSpace

Using Invoke-Command for Remoting

For a more streamlined approach using PowerShell remoting:

Invoke-Command -ComputerName remotecomputer {
    Get-WmiObject Win32_LogicalDisk -Filter "DeviceID='C:'" | Select-Object Size, FreeSpace
}

This command runs the specified script block on the remote machine and returns the results.

Handling Potential Issues

Drive Mappings and Task Scheduler

When running scripts under task scheduler, drive mappings might not be available. Ensure paths are correctly mapped or use UNC paths.

Access Denied Errors

Access to remote WMI objects may require additional permissions. Use credentials with sufficient privileges:

$cred = Get-Credential -Credential 'username'
Invoke-Command -ComputerName remotecomputer -Credential $cred {
    Get-WmiObject Win32_LogicalDisk -Filter "DeviceID='C:'" | Select-Object Size, FreeSpace
}

Advanced Approach Using UNC Paths

For a more robust solution that avoids some common pitfalls:

function getDiskSpaceInfoUNC($p_UNCpath, $p_unit = 1tb, $p_format = '{0:N1}') {
    Add-Type -MemberDefinition @'
        [DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)] 
        [return: MarshalAs(UnmanagedType.Bool)] 
        public static extern bool GetDiskFreeSpaceEx(string lpDirectoryName, 
            out ulong lpFreeBytesAvailable, 
            out ulong lpTotalNumberOfBytes, 
            out ulong lpTotalNumberOfFreeBytes); 
'@ -Name Win32Utils -Namespace GetDiskFreeSpaceEx -PassThru

    $freeBytes = New-Object System.UInt64
    $totalBytes = New-Object System.UInt64
    $totalFreeBytes = New-Object System.UInt64

    $result = [Win32Utils::GetDiskFreeSpaceEx]($p_UNCpath, ([ref]$freeBytes), ([ref]$totalBytes), ([ref]$totalFreeBytes))

    if ($result) {
        $total = $totalBytes / $p_unit
        $free = $totalFreeBytes / $p_unit
        [PSCustomObject]@{
            Path      = $p_UNCpath
            Total     = $p_format -f $total
            Free      = $p_format -f $free
        }
    } else {
        Write-Error "Failed to retrieve disk space information."
    }
}

# Example usage:
getDiskSpaceInfoUNC "\\remotecomputer\c$"

Explanation

• Add-Type: Loads a .NET assembly to use GetDiskFreeSpaceEx.
• UNC Path: Uses Universal Naming Convention paths for robustness.
• Error Handling: Checks if the function call was successful.

Conclusion

This tutorial provided methods to access disk capacity and free space on both local and remote computers using PowerShell. By understanding these techniques, you can efficiently manage storage resources across your networked environment. Always ensure you have the necessary permissions and configurations set up for accessing remote systems securely.