You have a choice of RAID volume sizes and how that RAID is configured. In a 4 stripe/drive configuration you can have 1.0 - 2.0 or 3.0 Terabytes of storage that wil give you around 240MB/sec of read and 220 MB.sec of write speed configured as a RAID 0. Eight stripes/drives will double that.
SATA RAID is very cost effective and has very fast sustainable transfer speeds. So, it depends on the format of video you are using and the number of video tracks you need active.