Some NVR's have different drive requirements for RAID 5.
If you are getting this warning, then the minimum requirements are below.
PRN-4011 for RAID 5 is a minimum of 5 HDDs.
XRN-2011 for RAID 5 is a minimum of 4 HDDs.
SRN-4000 for RAID 5 is a minimum of 5 HDDs.
SRN-1000 for RAID 5 is a minimum of 4 HDDs.