When tasked to automate a task, I rely on my scripting background to get the job done. Back then, it was all VBScript. Now that more and more customers are moving to Windows Server 2008 servers, I try to convince my customers to use PowerShell for all their scripting needs.

A few weeks back, a friend of mine asked me to write a script that will check the disks on all of their servers and send a report via email.  They have over a hundred or so servers in their data center and it will be a bit cumbersome to log in to each server just to check for free space on their disks. While their network operations center have access to reports generated by their monitoring tools, she didn’t. Which is why she opted to do it on her own. I tried to demonstrate why PowerShell was my scripting language of choice for this task by highlighting how this task can be done in a single line of code. Not that it can’t be done otherwise but this is an effective way to tell people how easy it is to use Windows PowerShell. Below is the script to do the task (BTW, this can be written in a single line. The blog engine just made it as it is due to space constraints)

Get-WmiObject Win32_Volume -computername “localhost” |

Select-Object __SERVER, Name, @{Name=”Size(GB)”;Expression={“{0:N1}” -f($_.Capacity/1gb)}},@{Name=”FreeSpace(GB)”;Expression={“{0:N1}” -f($_.freespace/1gb)}},@{Name=”FreeSpacePerCent”;Expression={“{0:P0}” -f($_.freespace/$_.capacity)}} |
Where-Object -FilterScript {$_.FreeSpacePerCent -lt 15} |
Sort-Object -property “FreeSpacePerCent”
Format-Table

Now this may seem intimidating at first but let’s disect the script to understand what it is doing. The Get-WmiObject cmdlet calls the Win32_Volume class to scan thru a list of disks (I’m using the -computer parameter to highlight an important concept later on.) This includes mountpoints, local drives and USB drives. If you’re only concerned about local disks and mountpoints, you can exclude USB drives by filtering via the DriveType attribute of the Win32_Volume class.

Get-WmiObject Win32_Volume -computername “localhost”

Since we are interested in the size of the disk, the free space in GB and in per cent values, we will use the Capacity and FreeSpace attributes of the Win32_Volume class. We do need to perform some calculations to make sure that we get the values we are accustomed with – GB for capacity and per cent in free space value. That’s what the calculations are for, noting that capacity and free space are expressed in bytes. The Select-Object cmdlet simply creates a new object by defining a new attribute from the original Win32_Volume class – server hostname, drive or mountpoint name, capacity and free space – named FreeSpacePerCent. This will definitely give you all the disks on a server with the defined attributes.

Select-Object __SERVER, Name, @{Name=”Size(GB)”;Expression={“{0:N1}” -f($_.Capacity/1gb)}},@{Name=”FreeSpace(GB)”;Expression={“{0:N1}” -f($_.freespace/1gb)}},@{Name=”FreeSpacePerCent”;Expression={“{0:P0}” -f($_.freespace/$_.capacity)}}

But we don’t want all of the drives. We only want those that have FreeSpacePerCent value less than your allowable threshold. In this example, less than 15 %. So, we use the Where-Object to filter the results.

Where-Object -FilterScript {$_.FreeSpacePerCent -lt 15}

As an administrator, we need to make sure that we address issues that are more critical than others. This is where the Sort-Object cmdlet comes in. We sort the results in order of increasing FreeSpacePerCent so we can immediately address those disks with very little free space left.

Sort-Object -property “FreeSpacePerCent”

Finally, the Format-Table cmdlet is just for aesthetics. The reason is because I will be sending the results of this script as an email attachment.

Now, that wasn’t so hard, was it? Understanding what each cmdlet is doing and how you can pipe the results to another cmdlet is the key to maximizing the use of PowerShell. But if you have a hundred or more servers, you wouldn’t want to copy the script on all of your servers and run it from there, would you? There are a few ways to accomplish this. One of which is to ue PowerShell Remoting. This will be another topic for a blog post as there is more to it than just simply writing and executing a PowerShell script remotely. What I opted to do here is simpler since I’m assuming that my friend nor I don’t have access to Active Directory to create Group Policies to enable PowerShell Remoting on all of the servers. Since the Get-WmiObject cmdlet has a -computer parameter, I can use that to execute queries against remote computers. What I can do is simply read thru a list – probably a list of computers in Active Directory or even as simple as a text file list. I opted for the text file list for the same reason that I didn’t go for PowerShell Remoting. So, what I did was to convert the script above to a function that I will call while passing values to the -computer parameter of the Get-WmiObject

function getDiskFreeSpace
{
Get-WmiObject Win32_Volume -computername $args |
Select-Object __SERVER, Name, @{Name=”Size(GB)”;Expression={“{0:N1}” -f($_.Capacity/1gb)}},@{Name=”FreeSpace(GB)”;Expression={“{0:N1}” -f($_.freespace/1gb)}},@{Name=”FreeSpacePerCent”;Expression={“{0:P0}” -f($_.freespace/$_.capacity)}} |
Where-Object -FilterScript {$_.FreeSpacePerCent -lt 15}  |
Sort-Object -property “FreeSpacePerCent”  |
Format-Table
}

I will call this function as I read thru a list of servers in a text file passing the computer names as parameters. And since I want the results of the query in a single output file, I used the Out-File cmdlet to save the results in a text file

ForEach($s in Get-Content C:serverlist.txt)
{
getDiskFreeSpace $s  | Out-File C:diskFreeSpaceResults.txt -append
}

Sending emails

I used a simple script in the past to send emails via Windows PowerShell. This was prior to PowerShell v2.0

$SmtpClient = new-object system.net.mail.smtpClient
$SmtpServer = “smtp.yourmailserver.local”
$SmtpClient.host = $SmtpServer

$From = “Friendly Reminder “
$To = “recepient@yourmailserver.net”
$Title = “Subject Matter”
$Body = “Body Text”


$SmtpClient.Send($from,$to,$title,$Body)

With PowerShell v2.0, the Send-MailMessage cmdlet was made available to send an email message. This made it easier to integrate sending email functionalities in PowerShell scripts. Adding one more line to the script above, I’ve included email sending functionality with attachment

Send-MailMessage -to “recepient@mail.com” -from “sender@mail.com” -subject “Servers Disk Free Space Report” -Attachment “C:diskFreeSpaceResults.txt” -SmtpServer “yourSMTPserver.mail.com”

Now, you can start using this script with a text file that lists all of your servers. Make sure that the server on which you will be running this script has Windows PowerShell v2.0 installed and that you can communicate with those servers. I’ve seen servers on different VLANs that are isolated from each other but are in the same Active Directory domain. This causes the script to fail due to connectivity issues. Check with your network administrator to be sure.