If you actually have 7.9 TB used, you are too low on space.
The most you should have used on an 8 TB drive is 6.8 TB. Beyond that, the system will be trying to repeatedly create temporary files to manage memory. If you are backing up date to iCloud it creates temporary files at the root folder, and if you are doing a Time Machine backup the same thing. The root folder is the primary folder when you open the hard drive in the Finder that shows Applications and Users.
This maximum has been found to be arbitrarily true across hard drive lineups based on a percentage of amount full being 85%. You can google the research, and it is pretty true across all platforms.
Instead of formatting, do a better job of filing files, and locate on your on drive backups. A backup is not a backup, until it is in two separate distinct physical locations at a time. When you duplicate folder on the same hard drive, that duplicate is not a backup. The whole purpose of a backup is reduce the risk sudden media failure of the entire failure. You would ideally want at least two separate distinct backups of all critical data in event you do get sudden media failure, and your backup is suddenly your only source of your data. Test your backups regularly.
What to backup....Apple's internet installers have recently disappeared and are not always available. As a result we recommend keeping backups of all license key preference files, installers not found elsewhere, personal documents, music file originals, and photo originals. A clone backup is ideal, as it replicates the entire drive to another drive. Time Machine is good for archival purposes, but only if do a restore to your system with your existing Time Machine backups to yet another drive with the same or newer operating system. If you don't and the backup drive fails, your Time Machine backup may be worthless.
