If you have any of the following models of AI NVRs:
The recording bandwidth is capped at 150Mbps unless RAID or Distributed Recording is implemented. When implemented this will increase the recording bandwidth to 400Mbps with the exception of the PRN-1605B2, where the bandwidth will increase to 250Mpbs.
To set up RAID 5 you will need 6 HDDs
If you have less HDDs than this on the NVR or you do not want to set up RAID, you can set up Distributed Recording instead. This feature allows you to record certain cameras on specific HDDs. You don't need a minimum number of HDDs to implement this as it will work with just one HDD
You can set up Distributed Recording in the Device->Storage Device->Distributed Recording section of the Settings menu