Where Did My Azure Disk Space Go?

I've written in the past about Azure backups failing due to size limits being exceeded. The _backup.filter file is a straightforward thing to use, but what do you do when you can't see what the cause of your file usage? The Azure Web Aps Disk Usage tool is an easy way to find the offending directory.

Azure Will Alert You About Failed Backups

Your team will be alerted when a backup fails, and show a summary of these issues in Azure under Monitoring -> Alerts.

Each record will have further details about the issue, so it's clear the Processing app is past 10gb of disk usage all of a sudden. Very odd since there have been no deployments, but I do know there's a support case open about Processing.

Activity log event description
CorrelationId: XXXXXX
Timestamp: 2022-12-12T18:00:04.1326017Z 
Creating temp folder. 
Retrieve site meta-data. 
Backing up the databases. 
Error in the backup operation: The website + database size exceeds the 10 GB limit for backups. 
Your content size is 10.3 GB. 
Try using a backup.filter file to exclude some files from the backup as described here 
https://aka.ms/partial-backup, or try removing the database portion of the backup and use externally offered database backups instead.

Finding the Offending Set of Files

What's the most efficient way to find large disc space usage? The Azure Web Aps Disk Usage tool will help you. In Azure, go to the resource -> Development Tools -> Advanced Tools, which will bring up Kudu. 

From here, navigate to Site extensions, switch to the Gallery tab, and search for “disk”.

You'll be given an option to install this extension, or in my case, launch it. Installation requires the app to restart, so be mindful of the time you're doing this.

This will bring up a view of your app's disk usage, where you can drill down and find out what's going on. You can then decide to use your filter file, or just delete the files if it's a temporary issue. In this case there's a tremendous amount of log files that I later found out was due to support putting the app in Debug. I've also seen a few cases where someone created a memory dump and never came back to clean it up.

Once the files have been taken care of you can go to your app's backups area and manually run the job to see it's working according to plan: