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. I think the answer is a big fat no. 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 filesystem. 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.
As mentioned in my previous post on snapshots and replication, 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 not management, reporting, or cataloging, other than what you get on the tape itself.
I just want to close out by saying that 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.
One thing's for sure: you can't do that with tape. 😉