As we all know, a sudden power outage has a greater impact on the computer. Especially on mechanical hard drives, data loss or non-reading may occur after a power failure. What are the characteristics of the mechanical hard disk structure that will cause it to be vulnerable to power failure? Today we talk about the topic of mechanical hard disk power off.
Mechanical hard disk power loss and loss of data principle
At present, the mechanical hard disk is mainly composed of a magnetic head and a magnetic disk. The magnetic head is a key part of the mechanical hard disk to read and write data. When the mechanical hard disk is working, the magnetic head will write track data or read existing data when the magnetic disk rotates.
When the mechanical hard disk is reading data, the magnetic head will constantly move inside the mechanical hard disk and contact with the tracks in different positions. Because the disk rotates at a high speed, a layer of rapidly rotating air is formed on the disk surface, which makes the magnetic head in flight state. ', did not come into contact with the disk, in this state, the head will not wear out with the disk surface, but also to achieve the purpose of reading data. In order to avoid head and disk contact wear, modern mechanical hard disk will have a head reset When the mechanical hard disk is not working, the magnetic head returns to the reset position. The magnetic head reset is not driven by electric energy, but mechanical power.
There is a spring-like device on the magnetic head, which always tries to pull the magnetic head back to the position area. When the power is turned on, the magnetic head moves to the top of the magnetic disk. If the mechanical hard disk suddenly loses power, the magnetic force disappears and the magnetic head is pulled back instantly, but the magnetic disk is stopped immediately. As a result, the air formed on the disk surface disappears, and the magnetic head easily falls on the disk surface, causing damage to the disk at the moment of being pulled back by the magnetic force.
practical testing
In order to restore the user's practical situation, we set up a platform to test the mechanical hard disk power off. The test scene is divided into standby and read and write data in two parts.
Standby power off
When the hard disk is powered off, the mechanical hard disk stops quickly and the mechanical hard disk drive on the computer is lost. After the hard disk is plugged in, everything is back to normal.
Read and write data interrupted
When reading and writing data, unplug the hard disk power supply. At this moment, the mechanical hard disk stops quickly, the mechanical hard disk drive letter is lost in the computer, and the data transmission speed is zero. After re-plugging the hard disk power supply, everything returns to normal, and part of the data in the copying is lost.
Hard disk test
After two hard disk power failures, we performed a simple read/write speed test on the mechanical hard disk. Through a simple test, we can see that the power failure has no effect on this mechanical hard disk and it can be used normally.
Why did the mechanical hard disk fail during the test?
As mentioned above, when the magnetic head of a mechanical hard disk loses its power, it will return to the head carriage due to the magnetic force. When it is pulled back, it is easy to scratch the disk. However, this is not absolute. Because most of the time suddenly loses power. When the speed of the disc is also reduced, the probability of scratching the disc is very low. Therefore, we have no mechanical hard disk failure during the test. But we must remember that the power-off protection of the mechanical hard disk can be omnipotent. If your data is very important, then the UPS uninterruptible power supply is the most secure way.
In the event of a sudden power outage, the UPS can provide enough buffer time to solve the problem, although the time will not be too long, but enough time for the normal shutdown of the system will not damage the hard disk. You can also add a layer of protection, is to let Set up a disk array, which is known as RAID. RAID 1 and RAID 5 are commonly used to protect data.
RAID 1 is a group of more than two sets of N disks that mirror each other. The principle is to store data on the primary hard disk and also write the same data on the mirrored hard disk. When the primary hard disk is damaged, the mirrored hard disk replaces the work of the primary hard disk. There are mirrored hard disks for data backup, so RAID 1 data security is the best at all RAID levels.
RAID 5 requires at least three hard disks. RAID 5 does not back up the stored data. Instead, it stores the data and corresponding parity information on the disks that make up RAID 5, and the parity information and corresponding data. Separately stored on different disks. After a disk data of RAID5 is damaged, the remaining data and corresponding parity information can be used to recover the damaged data.
RAID 5 can be understood as a compromise between RAID 0 and RAID 1. RAID 5 can provide data security for the system, but the protection is lower than mirroring and disk space utilization is higher than mirroring. RAID 5 has the similarity with RAID 0. The data reading speed is just because there is more than one parity information. Of course, for ordinary users, if there is less important data, more copies can be stored on other storage media, and RAID mode is not necessary.
Finally, we remind everyone that some friends think that if the SSD loses power, it will not lose data. This is not the case. If the SSD is powered off, it may cause the current to be disturbed and the main control will be lost. Therefore, the users who use SSDs are also Please don't cut off power. Although the principle of solid-state hard disk damage is less than the mechanical hard disk by several orders of magnitude, it still can not stop human failure.
