ARRI UDF CFast 2 Windows Bug - Solution?

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Posts: 1
Joined: Wed Apr 06, 2022 4:01 pm

Hello dear ARRI-Experts :)

Since November last year there is the known Problem of ARRI UDF on CFast 2 Cards with Microsoft Windows like descriped here:

viewtopic.php?p=3053&hilit=udf#p3053 ... 7e25262846

Is there any solution in prospect?
I would be very happy if the solution is not to permanently using an outdated operating system :/

I know that it is a peculiarity in the film industry to use a PC with Windows instead of a Mac with OSX but i would like to continue using it :)

Thanks a Lot!

Greetings, Silvan
Oliver Temmler
Posts: 66
Joined: Wed Aug 13, 2014 3:16 pm
Location: Munich, Germany

To clarify: This problem affected the compatibility of various UDF-formatted external drives with Microsoft Windows. This was not limited to ARRI UDF drives.

We did identify a solution, but were not able to fully resolve the issue, as Windows still may or may not mount the media – depending on a negotiation between the reader hardware and Windows, which determines if a memory card is attached as removable media or external disk.

Nevertheless, here's an alternative to completely rolling back your OS to a state pre November 22 2021.
We followed up on a report that the incompatibility was introduced with the update of a single system file. If this file is replaced with an older version, an ARRI UDF volume (Compact Drive and CFast cards) will mount again. We confirmed this to work for Windows 10 and 11 machines.

Important Note: This is not a proper solution, but a quick hack that temporarily restores functionality. Performing these actions requires admin rights.
Because we have no knowledge of other changes that were introduced in this file, we cannot rule out that these actions may have a negative effect on the system stability, functionality or security. We therefore cannot accept any responsibility for any damage that may be a direct or indirect result of this operation. Please do not perform these steps unless you understand and are willing to accept the risk!

The file you are looking for is called partmgr.sys. It is stored in C:/Windows/system32/drivers/

On Windows 11, you may see something like version 6.2.22000.348.
On Windows 10, you may see something like version 10.0.19041.1387

This file needs to be replaced with a working version, which you can typically find in the Windows update archives on your PC.
You should find the archived versions under C:/Windows/WinSxS/ or wherever your OS keeps its system update backups.

The last known working version for Windows 11 was 10.0.22000.71
The last known working version for Windows 10 was 10.0.19041.1110

I strongly advise against any attempt to download this file from the internet as this may present a severe security risk.
  • If you find more than one partmgr.sys with that version number, you are looking for the one that has about the same file size as the version you will replace (~200kB).
  • Before you can replace the non-working version in System32, you need to change its ownership from “TrustedInstaller” to e.g. Administrators and grant the Administrator full access rights.
  • Rename the non-working file and copy the OK version from the system update backup folder into the Windows/System32/drivers folder.
  • The last step is to reboot your machine and the drives should mount again.
Note that every update Windows installs may cause this issue to resurface until Microsoft decides to patch the file.
Oliver Temmler
Product Manager Storage Media
ARRI Munich
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