how to calculate surveillance video storage space and choose NVR recorder server?

When we design a IP CCTV surveillance system, we always need to calculate the video storage space, then choose NVR(network video recorder). As professional NVR supplier in China, Sysvideo use a practically case to show how to calculate video storage space and choose NVR server.  

Customer  Requirement:
Please send me the recording solution for 130 HD IP cameras with 120 days recording as per Qatar Police standards.
Notes: Qatar Police standards require recording is 720P@15fps, 120 days recording, use RAID5.

Sysvideo 's video surveillance storage solution:

1, the video storage space calculation

 Total video:  720@15fps: the average bitrate is 1.5-2.0Mbit / second, let's to use 1.8Mbit, so the total video is:
  1.8Mbit/s / 8 * 3600s * 24hours * 130pcs camera * 120days / 1024 / 1024 = 289TB

2. HDD requirement:

 if we use 4TB hardisk,so need HDD= 289TB / 4TB / 0.9 = 80 pcs

3. RAID 5 NVR Server Choose:

solution 1: if we use 8 HDD RAID5 NVR,  we need 80pcs HDD / (8-1)= 11.42<12 pcs NVR,  every NVR need to support  channels= 130 / 12=10.8<16ch,  so we can use 12pcs 8 HDD 16channel 720P NVR;
                 cost:  SNK0816RD * 12 =


solution 2:  if we use 16 HDD RAID5 NVR,  we need 80pcs HDD / (16-1)= 5.3<6 pcs NVR,  every NVR need to support  channels= 130 / 6=21.6<32ch,  so we can use 6pcs 16 HDD 32channel 720P NVR;

 cost1 (using 16 HDD NVR):  (SN-ISC5000-S + 4*HDMI card)* 6 =   * SN-ISC5000-S don't include HDMI output, need to plus HDMI card.
               
cost2 (using new NVR SNK1632RD): SNK1632RD*6=                        * NVR SNK1632RD built-in 2x HDMI & 1x VGA (can display different content)

The three options cost are almost same, but if use solution 1, the user can connect more monitor, and it is more rubbst, as I recommend, if the bugget is enough, you can use solution 1.