A friend asked the day before yesterday why the hard disk I bought is always smaller than the target capacity. This is indeed a practical problem, because when we do a monitoring project, when we calculate the hard disk, we often calculate it according to the target capacity of the hard disk instead of delving into Its actual capacity is a 4TB hard disk, and its actual capacity is often only 3.7TB. Why? Today we look at it.
First, why the capacity marked on the hard disk is different from the actual capacity
When we buy a hard disk, we will find that the actual capacity of the hard disk is smaller than the parameters. For example, when buying a 4TB hard disk, click on the computer properties to check the hard disk capacity. If the number of hard disks used in the monitoring project is large, then this gap is obvious. Isn't this a lie?
Hard disk capacity involves conversion between decimal and binary algorithms. Among them, hard disk manufacturers use a decimal algorithm to facilitate calculations, while computers use a binary algorithm. Conversion calculations are required between them.
Hard disk manufacturer decimal calculation:
4TGB = 4000,000MB = 4000,000,000KB = 4000,000,000,000Byte
Operating system actual binary calculation:
4000GB = 4096,000MB = 4194304000KB = 4294,967,296000Byte
1GB actual byte (Byte) calculation:
1GB = 1024MB * 1024KB * 1024Byte = 1,073,741,824Byte
Then 4TB actual capacity:
4000,000,000,000Byte / (1024MB * 1024KB * 1024Byte) = 3725.29GB = 3.72TB
Therefore, the hard disk capacity of 4TB, we can only count 3.7TB, we must pay attention to this monitoring project.
Monitoring hard disk vs ordinary hard disk
1. What is the monitoring hard disk first?
The monitoring hard disk is a hard disk specially designed for a data storage system that runs continuously all year round.
2.Monitoring hard disks vs ordinary hard disks
a, continuous working time
The monitoring hard disk is designed to work continuously for 7X24 hours (24 hours a day, 7 days a week).
The normal hard disk design works continuously for 5X8 hours (8 hours a day, 5 days a week)
If you use ordinary disks for all-day video recording, it is equivalent to let ordinary hard disks work "overtime and overnight" every day, and the service life will inevitably decrease accordingly!
b. Power consumption and heat dissipation
Monitoring hard disk ≤8W / disk
Ordinary hard disk ≥14.5W / disk
Low power consumption not only puts less pressure on the power supply, but also reduces the pressure on heat dissipation. It's easier to keep the "Calm" work with the monitor!
c. Starting current
Monitor hard disk ≤2.0 amps, optimize power configuration
Ordinary hard disk ≥2.8 Amp
The startup power is small, especially when used on a multi-disc recorder, so there is no need to worry about too many hard disks, and the startup current is too large, causing the power to burn out!
d.Seismic performance
Monitoring hard disks: professional seismic solutions for multi-disk systems
Ordinary hard disk: Does not consider earthquake resistance of multi-disk system
Hard disks are very resistant to vibration, but they also vibrate slightly when they are working. Monitoring the hard disk can avoid the impact of mutual vibration between multiple hard disks and prevent damage caused by vibration!
e. Transmission optimization
Monitoring hard disk: non-stop transmission mode, suitable for stream transmission.
Ordinary hard disk: intermittent transmission, suitable for file transfer.
The video transmission is a continuous stream of video, and the intermittent transmission mode of ordinary hard disk is not suitable for this continuous stream transmission, which may cause problems such as video freeze.
Third, the calculation of monitoring hard disk
Regarding the calculation of monitoring the hard disk, Weak Jun has mentioned it several times, but many friends have been asking for a long time, and here is a summary by the way.
1.Calculation formula and common code stream
Speaking of calculations, what are we going to calculate?
In addition to the number of cameras and the time required to record, there is another important value: the code rate! In general, the larger the resolution, the larger the code stream. For example, the 200W camera we commonly use, the code stream is 4MB / S, which is 4096kbps. Then knowing the code stream, time, and channel number, we can directly apply the formula to calculate.
The formula is as follows:
Bit rate × 3600 × 24 ÷ 8 ÷ 1024 ÷ 1024 = 1D (one day)
Common code streams:
Let ’s explain the value of this formula. 3600 seconds is 1 hour, 24 is 24 hours a day, 8 is byte, and 1024 is used to convert the code stream into MB. Therefore, to convert G, divide by 1024 If you change to T, you need to divide by 1024, which is 1 day of storage. How long does Party A need to store and multiply by the number of days?
The above is the calculation method of H.264, which is basically rare now, so let's look at the application of H.265 technology.
2.What is H.265?
First of all, h.265 is a new technology! H.265 is a technology that exists in cameras and video recorders. With the development of video surveillance technology and social needs, more and more pixels bring more than just an increase in clarity. There are also high hard drive costs and high bandwidth pressures. At this moment, H265 is here, reducing the code stream while ensuring clarity. Almost double the efficiency, which means that for general monitoring systems, H.265 can save nearly half of the storage space, while reducing the average network bandwidth.
For example:
Under H.264 technology, one month of 4 300W storage is approximately: 60G * 4 * 30 = 7.2T
Under H.265 technology, one month of 4 300W storage is approximately: 30G * 4 * 30 = 3.6T
This is still stored, let's look at the bandwidth again. In the past, if H.264 wanted to watch a 200W pixel high-definition picture remotely, it may require 6M uplink bandwidth, while under H.265, a 6M network can watch a 300W high-definition picture.
Therefore, the cost reduction is not only for hard disk storage, but also for switches.
Q. How do I use a device that supports H.265? Can I use the old camera to connect to the H.265 video recorder, and the storage can be halved? NO NO NO! For network cameras and video recorders, both parties must support H.265 technology.
3. How to calculate H.265 storage?
Ordinary h.264 2 million cameras are about 42G per day. Is that sufficient to divide by 2? actually not. Here's a cleaner way!
200W≈20G
300W≈30G
400W≈40G
In fact, H.265 is a compressed code stream, the same picture quality and the same bit rate, H.265 occupies 50% less theoretical space than H2.64. If conservatively estimated, you can press 60% of h.264 Store calculations.

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