Why does WQL LIKE operator not work on drive c, but works fine on drive d?

Question

I'm learning about File System Monitoring to speed up my 3rd and 4th backups of my mail server. I have a nice VB Script that works flawlessly on drive D, but when I query changes to drive C, nothing is returned if I use a wildcard.

Here are my queries:

This works fine for c:\sc, but does not return subfolder changes:

     Select * From __InstanceOperationEvent Within 10 Where TargetInstance Isa 'CIM_DataFile' And ((TargetInstance.Drive='c:' And TargetInstance.Path = '\\sc\\'))

This works fine for d:\sc, and does return subfolder changes:

     Select * From __InstanceOperationEvent Within 10 Where TargetInstance Isa 'CIM_DataFile' And ((TargetInstance.Drive='d:' And TargetInstance.Path LIKE '\\sc\\%'))

This one returns no changes at all. No error messages are returned, and the script continues to run:

     Select * From __InstanceOperationEvent Within 10 Where TargetInstance Isa 'CIM_DataFile' And ((TargetInstance.Drive='c:' And TargetInstance.Path LIKE '\\sc\\%'))

The double parenthesis are so that I can add similar queries connected with "OR".

My system drive is drive C.
Drive D is a removable USB drive.

Have I changed some setting on my system drive that is preventing this from working?
Or perhaps the query is returning too many results?

I have been searching about this for a few hours. Any insight will be greatly appreciated.

Answer 1

This is because when you uses the LIKE operator in a WQL sentence with the CIM_DataFile class, the WMI scan for the full drive to find a match, now since you USB drive have a more small (and simple) tree folder structure the WMI can return the results more quickly. but when you uses the C drive the WMI still running the Query until find all the matches. So the recommendation is don't use the LIKE operator with CIM_DataFile , instead just use the = operator like so :

Select * From __InstanceOperationEvent Within 1 Where TargetInstance ISA 'CIM_DataFile' And ((TargetInstance.Drive='c:' And TargetInstance.Path = '\\sc\\'))

P.D: If you are using the LIKE operator because you expect monitor changes in multiple folders, this is not possible, instead you must use one WQL and event watcher per folder.