Recently at IT Support Miami, one of our clients called in with an issue present on several of their computers. The client’s computers all had a significant amount of storage space suddenly occupied. These were 500+ GB hard drives that normally only held about 100 GB of data. Now the hard drives were almost completely full with only a few hundred KB of unused space.

The most perplexing part for our client was that the users of the computers reported not having downloaded any large files onto their computers. Of course they had downloaded a pdf file here and a Word document there, but nothing large enough to take up over 300 GB of free space.

Diagnosing the Issue

In order to diagnose the issue, our techs needed to download a small application to help visualize where the bulk of the data was located on the disk. The application they would be using is a lightweight storage analyzer called TreeSize. To clear up the necessary space for TreeSize, they copied some unnecessary files off of the computers and into our secured systems. They then deleted the copied files from the computers and downloaded the application.

Using the application, it was revealed that the bulk of the data was located in the folder C:\Windows\Logs. Once our techs saw this, it became obvious to them what the problem was.

Problem and Resolution

Pictured below are two screenshots of healthy versions of the problematic folders. If your computer’s folders look similar to those, then your computer is not suffering form this issue. However, if they appear as described above, then the following solution may work for you.

Screenshot of a healthy Windows computer's C:\Windows\Temp folder. There are no cab_* files present in the folder. In most cases, having one or two cab_* files present is still fine, but more than that can be dangerous.Screenshot of a healthy computer's C:\Windows\Logs\CBS folder. Importantly, only one CBS.log file is present in the folder. In an unhealthy folder, there would be several large CBS.log files.

The Windows operating system has a bug where it very rarely does not compress and remove certain log files as intended. The log files are temporary files which are generated by several Windows Operations like installing updates. Windows normally compresses these log files into cab_* files which are then deleted after about 24 hours. The problem occurs when a specific log file called “cbs.log” exceeds a size of 2 GB. A cbs.log file that large cannot be compressed into a cab_* file. When it is greater than 2 GB, the compression process fails and creates a garbage file. These garbage files are about 100 MB and are made once every 20 minutes due to the compression constantly failing. At this rate, 300 GB of space can be consumed in the span of about a month.

Our techs implemented the most effective solution to remedy the issue and prevent it from happening again in the future. First, they indexed to C:\Windows\Logs\CBS where all of the cbs.log files are located. They then deleted all but the most recent .log files in the folder. Once they had verified that all were deleted permanently, they indexed to C:\Windows\temp to find the cab_* files. They then permanently deleted ALL of the cab_* files from the folder.

After a quick reboot, our techs made sure that the cab_* files were not being generated any more than they typically should be.


IT Support Miami’s Enterprise Managed IT Security Services practice specializes in helping companies with their Enterprise IT Support needs. IT Support Miami provides both on-site and off-site IT supportOur team of technicians are highly technically trained to provide our clients with creative solutions. At IT Support Miami, we provide turnkey enterprise security solutions including on-site support, training, hardware and software selection, implementation and configuration, real-time monitoring, server setup and upkeep, data protection, user management, and Managed IT Security and network.  IT Support Miami is an expert in the field with more than 16 years in business and has a proven track record of successful managed IT services provider.

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