I would link on to previous posts and add following summary: "Backup is point-in-time copy-of-data which you can separate and take away from existing systems. This copy-of-data must allow you to perform restores during the defined protection period."
This implies that the backup must NOT have any dependency on production systems. This is possible to achieve with snapshots, or replications, but there are some question you need to ask, or protect against, eg.:
(a) is there any chance that the replication will replicate the errors to my secondary/backup systems?
(b) does the corruption in any previous snapshots prevent me to restore data from later ones?
(c) how hard is it to recover failed storage device to original status?
Especially for replicated systems using snapshots were you plan to have redundancy of snapshot data cross DC. e.g. you have 100-generations of snapshots, are you able to recover the storage with all those 100-snapshots, or you will just recover to one of these "point-in-times" loosing all other snapshots on this recovered site?
There is no ideal solution for everyone, at the end everything is balance of technology limitations, business needs, price tag and supportability.
The main reason why good-old-tapes are still in the game.