help in setting up external backup HDD for Macpro

hi guys,

not sure is this the correct place to post this.

On my 2008 Macpro Octo 2.8

currently has Raptor as my boot, 1 WD 1TB black as my working HDD and another WD 1TB black as my back up for my working HDD. and seagate 320GB as my itunes and media.

Question is, both my working and backup HDD is almost at full capacity.

so I'm thinking of setting up an external two bays NAS at raid 1 for double backups. Thinking of samsung 2T F3 HDDs. Sorry can't afford enterprise class HDD ~_~

As for the NAS connection... should I set up with SATA connection for just go for FW800?

Is this the correct route or there is a better solution?

Thanks in advance!!!