Progressive Perl for Windows: Using WMI to Request Data About Disk Drives

Last month, I discussed EventMon.pl, a script that monitors events in logs on remote Win32 machines and displays those events in realtime. The magic behind this script is Windows Management Instrumentation (WMI). In my explanation of EventMon.pl, I mentioned that you ought to become familiar with WMI. This month, I insist on it.

Many of you are probably rolling your eyes right now and moaning about yet another Microsoft technology to learn. WMI is well worth learning because it offers a rich set of features that will meet most of your administrative needs. With WMI, your Perl scripts can query a machine's settings, processes, hardware, and more. These scripts can even monitor events that a remote machine fires.

To help you learn WMI, I explain how to access WMI from Perl. In addition, I provide a practical example of how you can use WMI with Perl. I don't focus on the nitty-gritty but rather give a cursory overview of the information you need to start using this technology. . . .

I am using WMI with Perl, but whenever I access the logical disks using Logical_disk class, the script scans the floppy drives as well. I am trying to find a way so that I can get data only about logical disk without scanning floppy drives every time script runs (as this may damage floppy drives on the server, if I run the script very frequently).

Sanjeev Shukla June 17, 2002

You can use the ExecQuery() method off of the WMI Services script object to solve this. The query is very similar to SQL and would allow you to specify that you want all Win32_LogicalDisk instances where the DeviceID is greater than or equal to "C:". You could make more sophisticated queries such as collect all instances between drives D: and L:, if you like. Try this Perl code: 
 
<pre>
use strict; 
use Win32::OLE qw( in ); 
$Machine = "."; 
my $WMIServices = Win32::OLE->GetObject 
( "winmgmts:{impersonationLevel=impersonate, 
(security)}//$Machine/root/cimv2" ) || die; 
my $DriveCollection = $WMIServices->ExecQuery 
( 'select * from Win32_LogicalDisk where 
DeviceID >= "C:"' ) || die "Query Failed"; 
foreach my $Drive ( in( $DriveCollection ) ) 
{ 
my $FreePercent = int( ( $Drive->{FreeSpace} / $Drive->{Size} ) * 100 ); 
print "$Drive->{DeviceID}\n"; 
print "\tVolume: $Drive->{VolumeName}\n"; 
print "\tDisk Size: " . FormatNumber( $Drive->{Size} ) . "\n"; 
print "\tAvailable: " . FormatNumber( $Drive->{FreeSpace} ) . " 
($FreePercent%)\n"; 
print "\n"; 
} 
 
sub FormatNumber 
{ 
my($Number) = @_; 
my $Suffix = ""; 
if( $Number > 1024 * 1024 * 1024 ) 
{ 
$Number /= (1024 * 1024 * 1024); 
$Suffix = "G"; 
} 
elsif( $Number > 1024 * 1024 ) 
{ 
$Number /= (1024 * 1024); 
$Suffix = "M"; 
} 
elsif( $Number > 1024 ) 
{ 
$Number /= 1024; 
$Suffix = "K"; 
} 
$Number = sprintf( "%0.2f", $Number ); 
while( $Number =~ s/^(-?\d+)(\d{3})/$1,$2/ ){}; 
return( $Number . $Suffix ); 
} 
</pre>


Dave Roth August 23, 2002

We can find the drives on a machine using Win32_LogicalDisk and can find target lun bus numbers using Win32_DiskDrive . but how to find the mapping between the drive letters and targets/lun/bus .

Rahul Bhiide June 24, 2004

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