VSS Troubleshooting

I've had a few instances where clients have run into problems with their Exchange Writer during backup. Generally the end of their tale is that the writer shows a status of 8 when queried by the backup software and thus the job fails. One thing I have noticed about this retry-able error state is that its very vague, and what it means can vary greatly depending on what is showing up in your application log. However, I would like to provide some thoughts on a method for troubleshooting this effectively, as I've been doing a lot of trial and error myself.

Generally you want to start by checking at the highest level and here you want to make sure that you are meeting the minimum requirements to complete the backup. For our example here we'll just assume its an Exchange backup. So to start we'll want to check the Shadow Copy service itself. For this to function properly we will want to start the service and make sure its set to manual. While doing this also double check the volumes you are backing up and make sure you have at least 1GB free (assuming your data is larger than 1GB).

Now since this is a retry-able error another good thing to do is retry it. If you restart the Exchange Information Store service it should clear the 8 status from the writer and allow you to continue. If you get the same result, I then suggest re-registering the DLLs for VSS. If you go to this blog post you'll find something you can copy paste to build a batch file.

If we're still stuck with problems after these steps we need to take a look at the application log. Generally here you can reference the time of the failure on your backup solution with the appropriate event on the windows side. Sometimes you'll get something useful, sometimes you wont. If you find an Event ID that looks promising, honestly you will want to Google it at that point and cross your fingers that there is an easy fix. An example of this would be if you see events related to a failure of a 'volume dependency' which is just implying that your shadow copy is missing a portion of what you are backing up (in the case of exchange). You merely need to adjust your backup job to include all of the exchange volumes.

Once you've gotten this far it would be best to take advantage of a tool from the Shadow Copy service SDK. The tool is called vshadow and allows you to invoke specific writers based on the Writer ID, or the string for the name and other filters. It also gives a much more useful error message than what you have likely gotten thus far. You can find the technet article for it here. A simple example of this command goes as follows:


vshadow -tracing -wi={writer ID} [Target Volume]

This would include the writer specified during the shadow copy of the target volume, and do so in a verbose manner. You could also theoretically pipe the output into a text file for easier viewing.

While there is always more one could do in troubleshooting VSS, I've found these steps to be helpful as of late. If you have any strategies you've found to be particularly effect please feel free to share in the comments.

Ryan Koch
3X Systems
ryan.koch@3x.com