How much HDD for your CCTV .

Quite often people will ask two questions when it comes to the recording time of a DVR or NVR. The first would usually be something like “Do I have to erase the footage once the disk is full or will it re-write over itself ? ” Well that answer is easy and has been the same within the CCTV market for sometime now. ‘Auto Rewrite’ is an industry standard though there may be an option at times to turn it off when required. The second question would be “How long will my CCTV system ( the NVR/DVR ) record for ?” There is no one rule to apply on how long your CCTV system will record for or how large your HDD has to be. Here are a few of the factors to consider which will help you make the decision on storage size.

As a general rule you want to get 30 days footage on your CCTV system before it rewrites. 30 days gives you a bit of tolerance when looking for events. For example you may only notice an incident well after the time it occurred.  Someone may steal your favorite pot plant from the front but you did not notice until two weeks later. You may go away on holiday for a month and want a complete record of events for when you get back. It may be a case of catching out dishonest staff ; then you may need to look back over time and check for previous offenses or occurrences such as being late to work or general theft.

More activity means you will require more storage. How much actual motion activity is there on a camera at a specific location ? The CCTV cameras trigger recording by their predetermined motion detection settings. As a general rule if the picture’s pixels change by 5% then the system will start recording that camera. This ‘motion’ or as the system sees it ‘picture change’ could be triggered by a cloud passing over outside, your dog running in the back yard or just the wind moving a tree nearby. These examples are endless and this is the reason that camera placement is important as you want to capture useful information.  The main factor to consider here is how much ‘general activity’ is around that you want to capture over time. For example to capture footage at a 24hr store will require a lot more storage space than at a store that only opens for 8hrs a day. There will be a lot less activity on a domestic four channel CCTV system than what there may be on a commercial four channel CCTV system. In general  you will require more HDD storage for more active locations.

How much disk space ( HDD ) do I need then ? There are a lot of variables involved in calculating your available CCTV HDD storage time. These variable elements include : * The camera’s size in Mega Pixels ( MP ) * The frame rate of recording ( Real time motion is 25 fps )  * The quality setting for frames recorded * The video codec format being used ( ie New H265 format uses less space than H264 ) * The estimated hours of when motion will be present for any given camera in any given location. You can only really have a good ‘guesstimate’ at working this out. Going by our experiences you can use this simple guide :

  • Best estimated guide is in a domestic scenario using four 2MP cameras motion recording onto a 1TB drive.  On average this will give you between 25 and 35+ days of motion recording in ‘most’ cases.
  • Using this estimate you might also allow 500GB per 2MP camera connected and adjust accordingly for larger MP cameras and different motion scenarios. 

For example you have 4x 4MP cameras connected to your 4 Channel NVR.  For 30 day plus average record time you would calculate : ( 500GB x 2   per   4MP Camera ) x 4 Cameras = 4 Terra-byte ( 4TB )  in total HDD space recommended.

Consider the duty cycle and life of your HDD. The environment of the HDD in your CCTV system is a pretty harsh one. Your CCTV system will be recording something most of the time. The HDD does not get much chance to cool down. Compared to this to your PC at home where the hard drive gets to rest quite a lot and often is only ‘reading’ information hence it does not get worn out as quickly. You could compare the lifestyle of a HDD in a CCTV system to that of a taxi, it rarely gets turned off. For this reason it is an advantage to have a larger HDD fitted to your CCTV system. This will lower the ‘duty cycle’ of the HDD ;  the rate at which the HDD overwrites itself and hence extend its life. Another point to consider for larger CCTV systems is to have more than one HDD fitted. More than one drive recording alternates the recording cycle and gives each drive a chance to cool down. Also having two or more drives offers some ‘redundancy’ in the case of a disc failure ( ie > All your footage won’t be lost and the system may still record ). Please consider the physical environment of where you install your DVR/NVR for the life of the HDD. The HDD does get hot and having good ventilation and also a temperature controlled environment will extend the life of your system and HDD greatly.

Protect your HDD investment. You may have invested some good money into your CCTV system. In general the greater the Mega-Pixels, then greater the HDD size and then greater the money spent on your system. Some basic measures need to be in place to protect your investment. Firstly have a quality surge board in place as minimum protection and preferably have a UPS ( Uninterpretable Power Supply )  also connected. The UPS will also offer surge protection and protect against power failures plus ‘brown outs’ where under voltage and power fluctuations can harm electronic systems.  Consider physical protection for your investment against theft etc.  Once you invest in a better system with more HDD then it’s wise to keep it in an appropriate environment.

This article is only general in nature and intended only to explain that there is no real definite way to answer the question “How long will my CCTV system record for ?” …… though hopefully now you may have a better ‘crack’ at getting somewhere near the answer 😉


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