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Friday, May 23, 2008

File System Filters and minifilters

File system filters with the filter manager and minifilters are often overlooked, until a clash occurs when you've got several different products using these filters, such as anti-virus, file screening, offline archiving, quotas etc.

This post provides information on a few utilities I've used to identify the file system filters currently installed, and how you can then start diagnosing issues with the verifier.exe driver verification tool.

The commands below show the file system filters installed, their current altitude, and which volumes they’re attached to:

C:\>Fltmc.exe

Filter Name Num Instances Frame
------------------------------ ------------- -----
SAVOnAccessFilter
DfsDriver
Datascrn 0 0
FileScreenFilter 3 0
EvFilter 3 0
Quota 0 0

C:\>Fltmc.exe instances
Filter Volume Name Altitude Instance Name
----------------------------- ----------------------------- ---------------- --------------------
FileScreenFilter C: 260800 FileScreenFilter
FileScreenFilter D: 260800 FileScreenFilter
EvFilter C: 185100 EvFilter
EvFilter D: 185100 EvFilter

Debugging tools for Windows also has some file system driver diagnostics:

  • Install the debugging tools for windows (windbg)
  • Load windbg
  • Debug the kernel, using local connection
  • Load the filter kernel debugging extensions - .load fltkd
  • Use !fltkd.help, or specific commands from the articles below (!filters !volumes etc)

Once you have worked out which drivers are the file system filters and minifilters, you can then run verifier.exe on the machine to monitor the drivers. This enables you to record statistics such as memory paging and interrupts. Any number of the currently installed drivers can be monitored

How NTFS Works

Filter Manager and Minifilter Driver Architecture



Wayne's World of IT (WWoIT), Copyright 2008 Wayne Martin.

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About Me

I’ve worked in IT for over 20 years, and I know just about enough to realise that I don’t know very much.