That's a lot more involved. We're a quant firm that have servers colocated globally at various exchanges, so our data is distributed across a lot of systems. The main and original purpose of this storage system is to provide one centralized repository of all of this global data so that we can run backtests and perform analytics locally as opposed to having to hit our Australian system when we need ASX data, and then hit our German system when we need Xetra data, etc etc...
So different backups happen in varying directions, with the colocated servers using the main storage system to back themselves up, and the main storage system in turn backing portions of itself onto the colocated servers.
Not everything gets backed up, however, and most of what does get backed up can be compressed quite significantly. We mostly just back things up that can't be recovered from third parties or that are proprietary to our organization.
I mentioned I use rsync for backups.