1448 - How to manually test VSS

Redstor's backups rely on Microsoft's Volume Shadow Copy Service (VSS) for tasks such as change block tracking. When a backup fails as a result of a VSS-related issue, it may be useful to perform testing outside of your Redstor software in order to isolate the problem. This can be done using the Diskshadow tool, which enables you to run a VSS snapshot from the command line (i.e. with no connection to Redstor) to check if the problem persists. Read more about Diskshadow in this article on Microsoft's knowledge base

Follow the steps below to test VSS manually using Diskshadow.

1. From an elevated command prompt, run the following:

mountvol >c:\mountvol.txt

2. Open the text file. It will contain a lot of information but most importantly it will list the GUIDs for the relevant volumes, looking something like this:

\\?\Volume{GUID1}\
    C:\

\\?\Volume{GUID2}\
*** NO MOUNT POINTS ***

\\?\Volume{GUID3}\
E:\

\\?\Volume{GUID4}\
F:\

 3. Run the following:

diskshadow /l C:\diskshadow.txt
set verbose on
set context volatile
add volume \\?\Volume{GUID in format xxxxxxxx-xxxx-xxxx-xxxxxxxxxxxxxxxxx}\

Repeat the add volume line for each of your volumes, specifying the volume's GUID  in each case.

Add the following and run:

begin backup
create

4. This may take some time. Ideally, wait for at least an hour before running the following:

end backup

If the snapshot fails, you can eliminate your Redstor software as the cause of the issue.

If you are unsure which volume is responsible for the error, perform the test as above but with only one volume GUID at a time. Exit or reset Diskshadow between tests. You can stop once you have identified the problematic volume.

After running the Diskshadow tool, two text files will be created as outputs. You can consult these reports, as well as your Event Viewer, for details to help you resolve the issue. You can also employ tracing tools, as described here on Microsoft's knowledge base, to assist in gathering further information. For example, if you see the error "flush writes timeout", high levels of disk IO may be at fault, as suggested in this article on the Microsoft community.

Your best next step is then to open a ticket with your Windows support provider to assist you in resolving your issue.