Disk Array for VelHD

Hi, I am installing Vel HD. I currently have 1 external disk array using 8x500GB Sata drives with Rocket Raid 2322 card, using the miniSAS ports and cables (so called multilane). This array is not connected to the Vel HD card itself.

If the array is tested with AJA disk test it scores 550mb/sec read/write. But if we digitize clips using VelHD and the above array, it ran only for 30 secs and says the array is not fast enough. I doubt if it's the array, because I can digitize using other cards with same array without any problem, it even plays back 2K footages.

Any advice on this setup? Or do we really have to buy a Ciprico dual channel SCSI drives?

Any input will be greatly appreciated. I just don't want to unnecessarily spend money on another array.

Thanks

john