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The title of the question pretty much tells what is going on. If I disable the Unified Write Filter (UWF) on my Windows 10 IoT device the startup happens without any problem. It takes at most a minute, maybe a little bit more.

The problem happens when I have UWF enable. It takes at least 10 minutes to complete its startup sequence. It gets stuck at a screen saying "Please Wait" for almost the entire time. I can also see that it comes online fairly quickly. I can ping to it within the first minute.

At first I thought that it has something to do with the task I created in the task scheduler (since the enabling/disabling of the UWF happens via software), but when disable the task and turn UWF on manually via the command line this problem still occurs.

Is this problem directly related with the write filter? In any case, I have to use UWF (it is a work-related problem).

After doing some fixes (mostly related to a damaged disk), the boot time has shrunken to a little more than 5 minutes.

Update: I recreated an image following those exact steps, and this problem doesn't appear on the new image. Guess Windows is being Windows again!

marijnr
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3 Answers3

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The Microsoft article Common write filter exclusions has this information :

Some services and features write information to a device’s persistent volume, and expect that information to be present across device restarts. You may need to configure your write filter to allow for specific file and registry exclusions in order for these services and features to work correctly.

This topic lists registry and file exclusions that can help enable some common services and features to work correctly when write filters are enabled.

You need to add exclusions to all the registry keys and folders that are listed in this article.

To add a specific file or folder to exclusions, run the following command:

Uwfmgr.exe file add-exclusion c:\labs

Or

Uwfmgr.exe file add-exclusion c:\labs\report.docx

To add an exclusion for the registry key:

Uwfmgr.exe registry add-exclusion “HKLM\Software\My_RegKey”

To apply exclusions, restart your computer.

Prior to beginning maintenance (update installation, antivirus software update, copying of new files), you will have to switch to the special servicing mode:

Uwfmgr.exe servicing enable

Or it might be simpler to just turn off UWF.

My advice would be not to enable UWF for the system drive at all. If required, partition your disk to separate system and application. If that's not possible, you will need to find out and exclude the troublessome folders or registry keys.

For troubleshooting, UWF events, errors and messages are found in the Windows Event Log inside the Windows Logs\System event log.

More information may be found in the articles :

harrymc
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Seems UWF and Volume Shadow Copy have some problems working with each other, causing similar issues.

Check if you have Volume Shadow Copy active with vssadmin list shadows. If you have any shadow copies, delete them with vssadmin delete shadows.

robinCTS
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Fegyosz
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I had exactly the same behaviour and the culprit was a file exclusion.

I excluded the /winevt folder so that i could review the evt log upon e.g. a crash. This however slowed down the operating system significantly and a process 'runtimebroker.exe' kept using about 30-40% resources - even in idle state. Additionally i could not shutdown/restart - even with the UWF_filter functions. I presume the combination with uwf causes an endless loop somewhere.

I did by the way add all file exclusions noted in the 'common filter exclusions' tab.

So check all your exclusions and perhaps first test with the default settings. I feel like my case is somewhat close to yours seeing the symptoms you pointed out.

sommmen
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