Why is the current monitoring system easy to break the hard drive?

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The computer can't force the shutdown, otherwise it will damage the hard drive - I believe this is the initial understanding of many people about the use of the computer. In the example shown below, there are multiple forced power failures, resulting in serious damage to the storage hard disk and difficulty in recovery.

So, why does the forced power outage cause the hard disk data to be lost?

In general, the power-off protection of the hard disk is divided into two cases, a mechanical hard disk for large-capacity low-performance storage requirements, and a solid-state hard disk that is rarely used as a storage disk due to high price. When the mechanical hard disk is damaged, there will often be a blue screen of the computer, unable to start, and a large squeaking sound.

Based on this, we will discuss the principle of power failure of mechanical hard disk.

In 1973, IBM successfully developed a new type of hard disk IBM334, which has several coaxial metal discs, the disc is coated with magnetic material, these movable heads are sealed together in a box, the head can be rotated The change in the magnetic signal read on the disc - this is the ancestor of the hard disk we use today, IBM called the Winchester hard drive.

In addition to SSD (commonly known as solid state drive), most of the storage devices on the market are Winchester mechanical hard disk structures. The working mode is a phonograph in a confined space. The difference is that the distance between the head and the disc is only 10 nanometers. The movement of the head is slightly inadvertent and the disc is scratched. The power outage situation is included in the scope of “slightly careless”, and mechanical hard disk manufacturers have had a relatively mature power-off protection scheme after decades of exploration, so they rarely encounter strong security. The data is lost after the computer is damaged.

Comments from @杜渡渡鸟 (https://weibo.com/3219337542/FxelPmrD0) indicate that the previous monitoring system is a Windows industrial computer, you can go directly to the hard disk directory to delete a specified video, after clearing it can be expressed When the incident happened, the camera broke down and it was normal. Now mainstream monitoring devices (such as Haikang, Dahua, Yushi, etc.) are embedded operating systems. After the video compression is successful, you cannot delete a specified video. You must format the hard disk to delete all the videos. After the theoretical format. The hard disk data can be recovered. Of course, the specific recovery of the video depends on the hard disk's ideological awareness.

To put it simply, a very small "battery" is installed in the hard disk. At the moment when the external power supply is cut off, the mechanical hard disk will use the power of the battery to preferentially move the magnetic head to a safe area to avoid scratching the disc. This first ensures that a sudden power outage will not damage a large amount of data, and only lose a power outage is a small amount of data that has not yet been written.

Of course, in addition to the case of accidental power failure, normal aging, distance vibration, drop, and external force damage may cause damage to precision components and discs inside the disk. Once there is a situation where the hard disk is damaged and cannot be read, don't panic. The first thing to do first is to stop reading and writing the hard disk to avoid adding weight to the hard disk. Then, a professional data recovery organization is required to perform the "opening repair" - that is, the sealed hard disk is opened for targeted repair.

In general, hard disk repair has the following steps:

First open the hard disk in a dust-free working environment, replace the damaged magnetic head or other components in the hard disk;

Secondly, the newly replaced parts and the original parts are reassembled into a hard disk, and the corresponding firmware is debugged;

The magnetic field is then cloned, and the information in the damaged hard disk is completely copied to a new hard disk that is not damaged. This part is the longest in the entire data recovery. Depending on the degree of damage to the disc, it can take anywhere from a few hours to a month;

Finally, the data is re-combed in the cloned hard disk to extract the rescue data.

But don't worry too much. Cloud backup service provider BackBlaze publishes a hard disk failure rate report every year. In the 2016 report, 71939 hard disks for data storage are used as samples to calculate the failure rate of different brands of hard disks. From the perspective of the whole year, a total of 1,225 mechanical hard drives were damaged, and the average daily fault was 3.36. The annual hard disk failure rate was only 1.95%, which was significantly improved compared with 2.47% in 2015 and 6.39% in 2014. The technical upgrades of mechanical hard disk manufacturers are obvious to all.

Among the major brands in the statistics, Seagate hard drives (the hard drive brands involved in the cases listed at the beginning of this article) have the highest failure rate, and the SD4000DM001/ST4000DX000 are up to 31%. up and down.

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