About known issues with GitHub Enterprise Server upgrades
GitHub is aware of the following issues that could impact upgrades to new releases of GitHub Enterprise Server. For more information, see "Known issues" in the GitHub Enterprise Server release notes.
GitHub strongly recommends regular backups of your instance's configuration and data. Before you proceed with any upgrade, back up your instance, then validate the backup in a staging environment. For more information, see Configuring backups on your instance and Setting up a staging instance.
Required root disk size increased to 400GB
New installations of 3.15 or later, or upgrades to 3.15 or later require root disk size of at least 400GB. This capacity is an enforced requirement for the system to boot successfully. GitHub strongly recommends following the guidance in Increasing storage capacity.