WMI Filters allow you to select only computers that meet your chosen
criteria. Naturally, your Group Policy will only apply to the objects that match
your filter. For example, you want to assign an .MSI package, however you are
worried that disks on the XP workstations are full. The answer is design
and build a WMI filter.
Building WMI filters is a multi skilled task. You need to marry Group Policy skills with WMI knowledge. You also need to research which of Microsoft's Win32_Classes are suitable for a WQL (Windows Query
Language) query. As far as Group Policy skills are concerned there is a two stage process, creating the filter with its WQL query, then assigning, or wiring up the filter to the appropriate Group
Policy object.
Below is a WMI filter which checks the free disk space on the C: drive.
SELECT * FROM Win32_LogicalDisk WHERE (Name = " C:") AND
DriveType = 3 AND FreeSpace > 20000000 AND FileSystem = " NTFS"
Note 1: DriveType value = 3 means a local disk Note 2: 20000000 = 20MB. Note 3: Your Keyword - Win32_LogicalDisk
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A WMI filter consists a query that is checked against the WMI data on the
target machine, the answer is always true or false. Technically, you have created a separate object from the GPO in the directory. To apply it
to a GPO, you link the filter to the GPO. This is shown in the WMI filtering
section on the Scope tab of a GPO. Each GPO can have only one WMI filter;
however the same WMI filter can be linked to multiple GPOs.
Note that these WMI filters only work on Windows XP and later operating
systems. Windows 2000 and earlier clients just ignore any WMI filter and the GPO
is always applied to all objects. In effect it means that for these old
clients the criteria are always true so there is no filtering.
Here is a great idea to fine tune your Microsoft Group Policy and only apply the
settings where there is sufficient disk space. WMI filters are limited
only be your imagination, or your knowledge of WMI's Win32_Classes.
Troubleshooting
Group Policies is tricky
As an MCT trainer, I can thoroughly recommend TrainSignal because they
provide practical hands on training. In particular, I like the way TrainSignal cover all learning methods, instructor lead, video and of course text material. You can either take one module, for example Group Policy or go for
a combination of modules.
See more about Group Policy training here
