I don't believe disk arrays. Even you have great RAID protection, replication, snapshots there is still something called firmware. And it can have a bug. Usually it has (read release notes of next version) but fortunately not mandatory.
And there can be a bug screwing parity and this can be really bad.
You need to protect your disk based backups. I will describe you 3 different options by using of NetBackup:
- Multiple copies of backup job
- Storage lifecycle policies
- Own perl script using bpduplicate