arcserve-KB : How to change the altitude of the arcserve RHA minifilter driver

Last Update: 2016-04-25 13:47:37 UTC


Windows uses a dedicated set of load order groups for file system filter drivers and minifilter drivers that are loaded at system startup.  Legacy file system filter drivers can attach only to the top of an existing file system driver stack and cannot attach in the middle of a stack.  As a result, the start type for a driver and load order group are important to legacy file system filter drivers, because the earlier a filter driver loads, the lower it can attach on the file system driver stack. 

Arcserve RHA has a minifilter driver called 'xomf' and the purpose of this article is to explain how to change the altitude of that driver.  This is done in situations where the RHA minifilter driver may be interferring with another minifilter driver on the system.  If that is the case it is important to find out the altitude of the other minifilter driver and raise ours above the other.


To check the current altitude of our minifilter driver as well as the other minifilter drivers on the server do the following:

1. It is important to note our minifilter driver is only loaded when the scenario is running, if you do not want to run the scenario till we have changed our minifilter's altitude you can get our altitude from the registry instead of starting the scenario and then checking the alittude in a command prompt.  If your scenario is currently running you can get our altitude by bringing up a command prompt on the active host and typing 'fltmc altitude'. 

2. This will bring up a list of all the minifilter drivers on the system and their current altitudes.  Make note of the altitude for xomf and the other minifilter driver that may be interfering with ours.

3. Next, before changing the altitude I would stop the RHA scenario, then open the registry on this machine by going to start, run, and typing 'regedit'.

4. Find the following registry key:

Above we see the registry key starts with 'xomf8x64', the 8 is for windows 2008 and the x64 means this is a 64 bit host.  For windows 2003 32 bit the key would start with 'xomf3' , for 64 bit windows 2003 it would be 'xomf3x64'. 

5. At this point we are ready to change the altitude of our minifilter driver, if your scenario(s) are still running on this host I would recommend stopping them first.  Next, click on the registry key highlited above and in the right hand pane double click on the word 'Altitude' and a box will come up.  Change the numerical value of the altitude to a higher value than the minifilter driver you believe ours is conflicting with.  Make sure not to pick an altitude that is already being used, if necessary bring up the command prompt again that displays the output from fltmc instances.

6. After the new value is entered click ok and close the registry.  You can now start the scenario again and once it starts you can run fltmc instances again to see that xomf is now using the new altitude.

More info:

Here is an informative Microsoft document on load order groups and altitudes for minifilter drivers

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