How much storage do you really need for a CCTV System?


In this blog we run you through how to accurately determine Hard Drive sizes including:

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Camera Factors that Affect Storage Requirements

Using Dahua's Disk Calculator

Surveillance vs. Desktop Drives


Hard drives are often referred to as the ‘forgotten component’ of VSS/CCTV systems by the folk at Seagate and I cannot help but agree.

Everybody knows how important it is to specify cameras with the right lens for the right configuration, IR (infrared), Full-Colour, audio functionality, active deterrence etc., but what good is it all if the footage has been overwritten when you need it the most?

Or worse still, what if the drive develops a fault? (Spoiler alert: Seagate Recovery could get that footage back to you for free. Keep reading to learn more)

This blog is designed to help you understand how to calculate the required space your system(s) need, how to optimise your storage alongside the benefits of purchasing a pre-configured SkyHawk Surveillance drive with your recorders.


Camera Factors that Affect Storage Requirements
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Resolution

(Higher the resolution, the more space required)

Whether using a coax or an IP based system, all Dahua security cameras from us start at the 2MP resolution.

Simply put, 2MP means that the camera records each frame using 2 million pixels, whilst a 5MP uses 5 million, etc. Each of these pixels then need to be stored on the Hard Disk Drive meaning that each time you increase the resolution, more & more storage is required.


Bitrate

(Higher the bitrate, the more space required)

The main factor that affects the amount of storage space required is bitrate. Simply put, bitrate is the amount of information being captured and stored in kilobytes every second.

Without getting too technical, the higher the bitrate means the more information is captured every second, which means (in theory) a higher quality recording but also the larger the file becomes.

Bitrate can either be constant (CBR) or variable (VBR) with a maximum limit. It is much easier to workout the required space with CBR as the value remains the same. VBR can save space but it is near impossible to calculate accurately as the bitrate used per camera will depend on the scene and how busy it is.

However, it’s not quite as simple as just increasing/decreasing the bitrate, the video resolution, framerate and encoding also affect the overall quality of the captured footage and the required storage. Getting the right balance of each of these will help you capture the highest quality footage whilst also optimising the storage capacity of your systems.

A too high or too low bitrate for the resolution can result in either wasted storage space for little to no noticeable quality improvement or a blocky image from not enough information being captured for the resolution and scene.


For example, here is an 8MP Resolution with a 128kbps vs 8192kbps bitrate:

Click any image to view in full resolution (may need to zoom in).

(8MP Resolution @ 128Kbps)

(8MP Resolution @ 8192Kbps)

Proving that a bitrate too low, whilst you may be saving 64x the space, but at a severe quality cost to the end user.



Alternatively, below we demonstrate that with a bitrate too high, storage can be wasted. See a 2MP resolution below with a 2048kbps vs 8192kbps bitrate


Click the image to view in full resolution (may need to zoom in).

Do they look the same? We agree. Despite using 4 times the storage space, the quality difference is barely noticeable.

A good rule of thumb to find the optimal bitrate is to use 1024 bitrate times by the resolution of the camera. For example:

2MP = 1024 * 2 = 2048kbps
4MP = 1024 * 4 = 4096kbps
8MP = 1024 * 8 = 8192kbps

If using sub-streams, don't forget to include 512kbps for each camera.


Encryption

(The more encryption, the less space required)

These bitrates can then be further optimised by using H.265 encoding instead of H.264. H.265 is a recent addition to the industry and is available on most, if not all, Dahua cameras that we stock. Always refer to the relevant datasheet to check if unsure.

Keeping it simple, H.265 is more efficient at encoding the captured footage which means we can use a lower bitrate whilst still retaining the image quality.

For example, here is an 8MP image encoded with H.264 vs H.265, the difference is barely noticeable yet the H.265 is achieving the same level quality at half the bitrate.

Again, we don't see the difference neither. This shows that by simply changing to H.265 encryption, you could save up to 50% on your storage instantly without any difference to your end user.


Framerate
(Higher the framerate, the more space required)

Also known as FPS (frames per second), is the rate at which the frames that make up the video are refreshed. FPS can be simplified as the number of pictures a camera takes within a second and more pictures make a smoother video but requires more space.

A lot of Dahua cameras, particularly in IP, have capabilities up to 30 FPS which will result in smooth playback but often isn’t actually necessary and can impact the storage requirements of a system if using variable bitrate. For example, a 15 FPS recording will require exactly half the storage of a camera set at 30 FPS.

Typically, as you adjust the FPS you would adjust the bitrate accordingly to retain the quality. Technically, a lower FPS at a set bitrate would result in better quality frames in comparison to a higher FPS at the same bitrate (although to the human eye it may be indiscernible), the trade-off here is the smoothness of the video.

There is no correct framerate and this is often dependent on the requirements of the end user but below we have listed what is regarded as industry standards and used a video from Dahua above demonstrating the differences to let you decide what’s best:


High FPS (12-25FPS or above) – Appears smooth & fluent. 25FPS is considered 'Real Time'.

Low FPS (12 FPS or below) – Appears choppy and is often referred to as a ‘slide show’. Crucial information can also be lost in between frames for example if somebody runs past.


Once you have balanced out the above parameters to give you the desired quality of footage, the final piece of the puzzle is how / when you are recording. Many people like having continuous recording and in some cases (for insurance purposes) it is required, however most of the recorded footage there is nothing of interest and the footage is just taking up valuable hard drive space.

Simply changing from continuous recording to motion / SMD based recording could half the amount of storage required and further still if you only record intelligent events such as intrusions or tripwires.

Using Dahua's Disk Calculator

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Part of the Dahua Toolbox (which can be downloaded here: Dahua Toolbox), the Disk Calculator makes calculating storage a piece of cake.

Using each of the factors I have explained above, the Disk Calculator can determine the storage requirements for the required amount of time. You will see that you can specify in hours the amount of time that the cameras will be recording each day:


Using continuous recording = 24 Hours (or your scheduled recording time)

Using motion recording = 12 Hours (This will vary but is a safe guideline)

Using AI / IVS recording = 6 Hours (This will also vary and depends on the scene)


The calculator likes to predict bitrates, remember to change these to the settings you will be using.

It is always best to calculate using a worst-case scenario method, I.E H.264 encryption with the highest bitrate. This means that once you head to site, you have the flexibility to change encryption, adjust bitrates to save space if it's needed once you're there. Overestimating storage like this saves you from needing to replace hard drives in case you need to squeeze additional days out of the storage or if you need to add more cameras to the system later down the line.


Example Scenario

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Let's put the Disk Calculator and everything we've discussed so far into practise with a typical residential, 4-channel scenario. We will demonstrate sub-optimal vs. optimal settings and assume we have the following requirements:

  • 4x 4K Cameras
  • At least two weeks' worth of recording
For 24-hours continuous recording:
  • H.264. 8MP. 30FPS. 8192Kbps  4725GB (6TB Required)
  • H.265. 8MP. 30FPS. 4096Kbps  3000GB (4TB Required)

For 12-hours SMD motion recording:
  • H.264. 8MP. 30FPS. 8192Kbps  2362.50GB (4TB Required)
  • H.265. 8MP. 30FPS. 4096Kbps  1500GB (2TB Required)

For 6-hours IVS event-based recording:
  • H.264. 8MP. 30FPS. 8192Kbps  1181.25GB (2TB Required)
  • H.265. 8MP. 30FPS. 4096Kbps  750GB (1TB Required)

Remember that figures from the Disk Calculator are theoretical using constant bitrates which you will need to copy across when configuring your camera(s). Continuous recording should be very accurate whilst motion & event-based recording results will always vary and our 12 & 6-hour figures are the baselines that our Technical team recommend.


Surveillance vs. Desktop Drives
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Believe it or not but hard drives aren’t created equally. Some drives are specialised for games consoles, servers, desktops and surveillance drives are specialised in the same way.

Hard disk drives, no matter the application, have the following essential functions which are engineered to suit:


Writing Data – Storing & editing files

Reading Data – Opening & accessing said files

Workload – Rating of how much data (terabytes) that can be transferred annually reliably


Consider the stress that a hard drive in a recorder goes through: In most cases they are being constantly written to with high resolution recordings for 24 hours a day for years on end without any reboots or downtime. Seagate report that CCTV surveillance represents up to 95% of the drive’s operation.

Compare this with the hard drive in an office PC. Most PCs operate around 8 hours per day and their specifications are biased towards read capability and small data transfers such as saving documents & downloads alongside opening said documents and images. This workload is much closer 50/50 read & write and with much less data being transferred (think megabyte files to terabyte recordings!).

SkyHawk & SkyHawk AI are Seagate’s brands of specialised surveillance drives which are price-protected and available through Mast alongside your recorders. SkyHawk drives feature industry-leading workload ratings and is the key spec to look out for when choosing your HDD. Compare their workloads below with the type of drive that will be in your computer below:

 

Type of Drive

Typical Desktop

SkyHawk

SkyHawk AI

Capacities

N/A

1TB, 2TB

4TB, 6TB, 8TB, 10TB, 16TB

Workload

60TB /year

180TB /year

550TB /year

 

Exceeding the workload is effectively shortening the life of your hard drive so whilst a desktop drive may be able to work overtime to compensate in a recorder, you may find yourself back on site replacing said drives much sooner than expected.

SkyHawk drives over feature 3-years warranty whilst 2TB and above include their free Data Recovery service. Learn more about these services below:



Why Pre-Installed from Mast?

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Convenience Factor - Our Warehouse operatives save yourself the time of physically installing & initialising the drive.

Firmware Upgrades - With features & technology constantly evolving, vital firmware from Dahua is often released after the recorder is manufactured. Our operatives are instructed by our Technical Team to update recorders with specific firmwares to ensure all advertised features are available to you out of the box.

Peace of mind - Arguably the most invaluable benefit to purchasing pre-configured is that you know you or your engineers can get to site with confirmation that their CCTV recorder & HDDs are configured & proven to be operating out of the box. Whilst it’s unlikely you’d need to reschedule the job due to a faulty model on arrival, purchasing pre-configured removes all doubt.

End User Guide - A free add-on to each pre-config which is designed to save you & your customer's time on unnecessary calls & queries by providing how-tos on all the basic functions of their brand new CCTV system. It also includes space to leave your company details, SN & installation date in case the info doesn't answer their question.


See our full pre-config service on YouTube here: Watch Here


XBOX COMPETITION!

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Be sure to check out our latest competition to put all this into action!

[Running from August 1st - August 31st]