When you host your own NextCloud instance, you are responsible for backing up your data, ideally following the 3-2-1 rule. The 3-2-1 rule states that you should always have three copies of your data, two copies locally which are on separate devices and 1 copy off-site. Many users using a RAID array or distributed file system such as NFS or ZFS mistakenly believe they don’t need a backup. In fact that couldn’t be further from the truth, because RAID is not backup. Even though RAID can usually save you when one or two drives fail in your array, it cannot prevent data loss from some calamities, such as a failed RAID controller or a natural disaster.
One of the easiest ways you can back up NextCloud to an off-site location is by using an object storage service, such as Amazon S3 or BackBlaze B2. Both services provide a command line interface that supports a rsync-like sync command which can incrementally backup your data to cloud storage.