ByWake Mcelroy 2020-01-20 1017
1, forced power outage or forced shutdown has no effect on the hardware of the hard disk, but the hard disk can make use of the rotation of the disc after the power outage to return the head. But it will have an impact on the integrity of the data. Generally speaking, the write cache setting is enabled by default to enhance the write performance of the hard disk. After an abnormal power outage, the write of the hard disk will be terminated, the cached data will also be lost, and data integrity may be affected. This is also the main reason why some small partners do not recognize the disk after being turned on after a forced power outage. However, there is a live static for 30 minutes can be saved. It is also important to note that power is cut off while writing, which is likely to lead to an increase in the number of bad blocks, but fortunately, there are basically redundant blocks to replace when planning solid state drives.
2, the power loss of flash memory particles during the Program process may result in some page damage that can no longer be used; these damages will be bypassed by the algorithm of the internal controller to prevent SSD from becoming bricks, but the inevitable SSD life will be affected.
So, next we need to understand the principle of mechanical hard disk to prevent the loss of power outage data, here the editor gives you an example: Toshiba adds a flash memory chip that can only be used on solid-state hard disk on the latest 10TB enterprise mechanical hard disk. In the case of power outage, the inertia power generation with the help of disk rotation is used for the main control to transfer the data in the DRAM cache to the flash memory for safe preservation, which perfectly realizes that the power-off data is not lost, and the planning is very ingenious.
For enterprise SSDs, the power supply of power-off protection capacitors is generally added to the emergency write of data in the cache. However, this operation makes the life of the capacitor more limited, and some of them may be destroyed before the flash memory so as to cause inestimable problems, so this function is not set up in the home solid-state hard drive. On the other hand, the DRAM cache of SSDs mainly stores FTL flash mapping table, which only supports the maximum 16MB capacity to cache the data read and written by users for a short time. With the issuance of the Flush instruction, this part of the data will be written to NAND flash memory for permanent preservation.
Flush instruction is sent automatically and regularly by the Win system, which forces the data in the solid-state disk cache to be actually written to the flash memory for permanent storage. The ToshibaQ200 240g solid state drive is used for the test below. Q200 is one of the most cost-effective Toshiba original 8-channel MLC flash SSD, SSDs.
Use manual Flush software called sync to verify the function of the Flush instruction:
The power is cut off immediately after the file copy is completed, and the file MD5 will make an error after rebooting, because there is still some data left in the cache and not actually written to the flash memory:
If you execute the Flush command after the file is copied, and then immediately lose power, verify that the MD5 is correct again, indicating that the file has been fully written to the solid state drive.
Win systems automatically send Flush instructions to SSDs at a high frequency, so occasional forced shutdowns are not necessarily a problem. In addition, the power-off protection of the home computer has little to do with the presence or absence of DRAM cache: even if you can protect the hard disk cache data, if the host does not have UPS uninterrupted power supply, the main memory data will still be lost, and the instructions sent to the SATA interface immediately after the power outage may also be wrong.
The main goal of power-off protection of household solid-state hard disk is to prevent flash memory from flying and destroy the original data bit content of the same unit. ToshibaQ200 mainly uses Copy on Write to achieve protection: as shown in the following figure, when a solid-state disk wants to modify Page 3, it will first copy the original contents of Page 3 to the reserved area, and then write the data of Page 3. If the write is interrupted by a power outage, the solid-state drive can also be recovered from the data copied in advance.
The above experiences and theories all clear that forced shutdown is harmful to SSD, so when using SSD, friends had better not often forcibly cut off power to SSD, which may have unexpected things to happen, and occasional forced power cuts do not have to worry too much, SSD can work normally.
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