Backups have two distinct purposes. The primary purpose is to recover data after its loss, be it by data deletion or corruption. Data loss can be a common experience of computer users. The secondary purpose of backups is to recover data from an earlier time.
I’m a fan of putting backups and recovery on disk. I’m even a bigger fan of backing up in such a way that a “recovery” can simply be done by using the backup as the primary while the real primary is being repaired. It offers the least amount of downtime in some sort of disaster.
But this does beg the question of whether or not leaving the backup in the same format as the original leaves it vulnerable in some way that putting it into a backup format doesn’t. Specifically, I’d say that a copy is no more of less susceptible than a file on disk that’s in some kind of “backup” format. Either one could be deleted by a malicious admin, unless you were storing it on some kind of WORM file system. The same is true of backups stored on tape. If someone has control of your backup system, it doesn’t take a rocket scientist to quickly relabel all your tapes, rendering them completely useless to your backup system.
What makes something a backup (versus just a copy) is not its format? The question is whether or not it has management, reporting, and cataloging built around it so that it is useful when it needs to be in that sense, a CDP or near-CDP style backup is actually more of a backup than a tar tape, assuming the tar tape is just the result of a quick tar command. The tar tape has no management, reporting, or cataloging, other than what you get on the tape itself.
Backup products that are making instant recovery a reality are my favorite kind of products. These include CDP and near-CDP style products like Simpana, Zerto, Veeam, AppAssure, RecoverPoint, and any of the storage array or storage virtualization products that accomplish backup via snapshots and replication. This is the way backup should be done.
Backup continuously or semi-continuously, and recover instantly by being able to use the backup as the primary when bad stuff happens.