How does gitaly instructed backup work

https://docs.gitlab.com/ee/administration/backup_restore/backup_gitlab.html?tab=Linux+package+%28Omnibus%29#create-server-side-repository-backups

How does this new feature work?

The question we have is:

Does the gitaly server needs additional storage available to actually create this backup, or unlike the other backup gitaly directly writes to s3 without the need of creating artifacts?