Re: Help with a repurpouse rebuild
How much data do you currently have stored?
If you have 16TB worth of data, you want your backup destination to be twice that size IMO, which means you will need 32TB worth of storage on the backup server.
Next, you will have to use RAID obviously, but, 4TB disks are not exactly something you want to be using in RAID, a 3x4TB RAID5 array has a high chance of being rebuilt should a disk fail. You also need to consider the RAID controller, you shouldn't be using software based methods, or cheap generic controllers, a good controller is going to set you back a minimum of $400 + $100 for the BBU.
Most people that need backups end up going with cloud services, sure it takes forever to backup, but, it's more reliable, cheaper in the short-term, and you don't have to worry about equipment failures. It only takes a single bolt of lighting to destroy your main file server, and your backup file server if they are in the same area.