November 26, 2023

Why is declared capacity of hard drive different from actual capacity? How to calculate hard drive monitoring?

ForewordHello everyone, I'm Mr. Lin. The day before yesterday, a friend asked why hard drives we buy are always smaller than standard capacity. This is indeed a practical issue. , because we do When monitoring projects, when calculating a hard drive, it is often calculated according to target capacity of hard drive, rather than delving into its actual capacity. A 4TB hard drive often has an actual capacity of only 3.7TB. . Why? Let's see today. Text1. Why is declared capacity of hard drive different from actual capacity

When we buy a hard disk, we will find that actual capacity of hard disk will be less than parameter mark. For example, when purchasing a 4TB hard drive, click computer properties to view hard drive capacity, and find that capacity is only 3.72TB, which is 0.28TB different from 4TB capacity. If we use a large number of hard drives in monitoring project, then gap will be obvious. Isn't that a lie?

Hard disk capacity depends on decimal and binary conversion. Among them, hard drive manufacturers use decimal arithmetic to simplify calculations, while computers use binary arithmetic and conversions are required between them.

Decimal calculation of hard disk manufacturer:

4TGB=4000,000MB=4000,000,000KB=4000,000,000,000 bytes

The actual binary computation of operating system:

4000 GB = 4096,000 MB = 4,194,304,000 KB = 4,294,967,296,000 bytes

Calculating actual byte(s) for 1 GB:

1 GB = 1024 MB * 1024 KB * 1024 bytes = 1,073,741,824 bytes

Then actual capacity is 4 TB:

4000,000,000,000 bytes/(1024MB*1024KB*1024bytes) = 3725.29GB = 3.72TB

So, we can count only 3.7TB out of 4TB hard drive capacity, which we should pay attention to in monitoring project.

Second, monitoring hard disk compared to a conventional hard disk

1. First of all, what is hard drive monitoring?

The monitoring hard drive is a hard drive specially designed for a storage system that runs continuously all year round.

2. Monitor hard drive compared to normal hard drive

a. Continuous working time

The monitoring hard drive is designed to operate continuously for 7 hours 24 hours (24 hours a day, 7 days a week).

Regular hard drives are designed to run continuously for 5x8 hours (8 hours a day, 5 days a week)

If you use a regular hard drive to record all day long, it's tantamount to making a regular hard drive "work overtime and all night" every day, and lifespan will inevitably be shortened accordingly!

b. Energy consumption and heat dissipation

Hard drive monitoring≤8W/disk

Normalhard disk ≥14.5W/disk

Low power consumption not only reduces load on power supply, but also reduces load on heat dissipation. The dashboard is easier to maintain a "quiet" work!

c, starting current

Hard drive monitoring ≤ 2.0 amps, power configuration optimization

Typical hard drive ≥ 2.8A

The starting power supply is small, especially when using it on a multi-disk DVR, you don't have to worry about too many hard disks and too much starting current, which will burn power supply!

g. Earthquake resistance

Hard drive monitoring: professional anti-seismic solution for multi-drive systems

Regular hard drive: don't consider shock resistance of a multi-drive system

The hard drive is very afraid of vibration, but hard drive itself will vibrate slightly during operation. Hard disk monitoring can avoid influence of mutual vibration between multiple hard disks and prevent damage caused by vibration!

e, transmission optimization

Hard Disk Monitor: Continuous transfer mode suitable for streaming.

Regular HDD: intermittent transfer, suitable for file transfer.

Video transmission is a continuous stream of video, and intermittent transmission mode of ordinary hard drives is not suitable for this continuous stream transmission, which may cause video freezing and other problems.

Third, keep an eye on your hard drive calculations

About calculating hard drive for monitoring, Mr. Weak Electric mentioned this several times, but many friends kept asking about it, and by way, I will summarize here.

1. Calculation formula and total bitstream

By way, what do we use for calculations?

In addition to number of cameras and time it takes to record, there is another important value: bitrate! Generally, higher resolution, higher bitrate. It is 4 MB/s, which corresponds to 4096 kbps. Then, knowing code stream, time, and number of channels, we can directly apply formula to calculate.

The formula looks like this:

Bitrate×3600×24÷8÷1024÷1024=1D(one day)

General code flow:

Let's explain meaning of this formula. 3600 seconds is 1 hour, 24 is 24 hours a day, 8 is bytes, and 1024 is unit of converting code stream to megabytes, so to convert G, you need to divide Let's take 1024, if you change to T, then you need to divide by 1024, this storage capacity for 1 day. How long batch A should be stored, then multiply by number of days, all right.

The above is H.264 calculation method, which is currently rare, so let's look at 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 VCRs. With development of video surveillance technology and socialHigher and higher pixels not only improve clarity, but also bring high hard disk costs and high bandwidth usage. At this point, H265 comes in, which lowers bitrate, ensuring clarity. The efficiency is almost doubled, that is, for a general monitoring system, H.265 can save almost half of disk space and reduce almost total network bandwidth.


With H.264 technology, four 300W storage in one month is approximately: 60GB * 4 * 30 = 7.2TB.

With H.265 technology, four 300W storage in one month is approximately: 30GB * 4 * 30 = 3.6TB.

This is still stored, let's take another look at throughput. In past, if you want to remotely watch a 200W HD image using H.264, you may need 6M uplink bandwidth, but in H.265, you can watch a 300W HD image on a 6M network.

In this way, cost savings occur not only on hard drive, but also on switches.

Ask how to use H.265-enabled equipment? Is it possible that if I connect an old camcorder to an H.265 DVR, memory capacity will be halved? NO NO NO! For network cameras and NVRs, both sides must support H.265 technology.

3. How to calculate H.265 storage?

A typical 2M h.264 camera is about 42GB per day. Is it possible to just divide it by 2? not at all. A shorter method is coming!




Actually, H.265 is for codestream compression. With same image quality and same code rate, H.265 takes up 50% less storage space than H2.64 in theory. can use h.264 60% data storage.

Lastly, I'll tell you a simple method. There are many calculation tools on Internet. Just find camera input parameter and it will come out immediately. You don't need to calculate it like that.