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OS Layer WMI Extensions


Hello all


We have a installed on the OS layer some WMI Extensions required for a monitoring software.. it has been working so far.


But in testing a new versions it seems that when the WMI extensions are updated on the OS layer they are not updated on the resultant template, the extensions have never been installed on any other layer.


So it seems that while we have updated the extensions on the OS layer the remain "cached" on the application layers as I created an new version of an app layer with the new version of the OS Layer but wmi still showed the old extension even when the OS layer used to create the app layer was on a newer version.


Is this expected? 


Should't it be treated like an OS patch?



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WMI is implemented with a database based on files.  If the WMI schema is changed that goes into the database.  If you change the WMI schema in multiple layers then the WMI Database from the layer with the highest priority will be the one used in the resulting published image.  That sounds straightforward but there are wrinkles.  If you build a layer with a version of the OS layer that you have added WMI schema updates to, then an app in that install modifies the WMI schema the underlying WMI database will be pulled up into the layer you are adding then the schema update will be made so in that layer you will have the changes previously made to the os layer plus any changes made during the layer creation. 


If you save that layer and deploy it and the platform layer has no WMI schema changes in it then all will be good.  But if you then go back and add a version to the OS layer and modify the WMI schema and deploy the same layers again those changes will not make it to the image because the app layer you created earlier was not updated and app layers all have a higher priority than the OS layer. 


So if you always added any app that requires a WMI schema change to a WMI app Layers that might work as long as the platform layer never gets a WMI schema update.  However with Citrix i think the VDA install modifies the WMI schema to add Citrix specific counters.  That means the changes you make that are not in the OS layer or are made after you create the platform layer will be overwritten by the platform layer.  So the safe way to manage apps that modify WMI are to either always install them into the platform layer or install them in the OS layer and recreate your platform layer any time you make a WMI change to the OS layer.


Just remember this is only for apps that modify the WMI schema.  Apps that just use WMI are not affected.


Hope this helps.

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