Failover cluster backup advice

Hi.

I have a brand new failover cluster, 2 hosts which are identical connected to a SAN with about 15 hyper v servers, inc exchange 2010, a storage server and SIMS.

Obviously this has quite a decent chance of surviving hardware wise all but a fire or flood. I want to now ensure we have a data backup to another building on site ( not sure if that is classed as offsite as such!)

Currently I run a windows backup to the newest old standalone server (if you see what I mean!) which then backs up its data to an external HDD.

However this seems a bit crap. I was thinking of using veeam? But to back up to what? I have 5tb available space on the cluster, so would I need that space in a nas or something?

I have Dpm installed but it seems to not want to let me backup to my nas shares?

Just need a bit of advice please.