The real factor affecting the life of SSDs: write amplification
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As TLC flash memory particles gradually occupy the high ground in the market, the life span of solid-state drives has once again been brought to the stage, and people are arguing, just like when SLC became weaker and MLC became the mainstream. It can be said that "I watched him go up to a high building, I watched him entertain guests, and I watched his building collapse." Everything is like this. Any new thing that replaces the old will go through a process from questioning to repetition and then to acceptance. Of course, today we are not going to discuss the question of which is better, SLC/MLC/TLC, but since we are talking about the life of solid state drives, in addition to the physical properties of flash memory particles, which play a deterministic role, the existence of the write amplification mechanism in the main control is also a key factor affecting the life of solid state drives. Write amplification mechanism So, what is the write amplification mechanism? How does write amplification affect the life of solid state drives? Next, I will talk to you about write amplification. Write amplification, also known as Write Amplification in English, was first proposed and used in public documents by Intel and Silicon Systems (acquired by Western Digital in 2009) around 2008. This term actually describes a multiple relationship between the target write value and the actual write value of the solid state drive, and is expressed in Arabic numerals. The smaller the write amplification value, the more it can improve the life of the solid state drive. To fully understand write amplification, we need to first understand the read and write mechanism of solid state drives. We know that the storage unit of a solid state drive is composed of flash memory particles, and it is impossible to achieve physical data overwriting. It can only be erased and then written, and the process can be repeated . Therefore, we can imagine that in the actual reading and writing process, the reading and writing of data will inevitably be erased and written multiple times on the flash memory particles, especially when some blocks are completely filled. The ratio of the increased number of writes and the original number of writes required by these multiple operations is the so-called write amplification. Therefore, a high write amplification value will reduce the life of the solid-state drive. (Solid-state drive flash memory particles have a rated P/E value, that is, the maximum number of reads and writes. High write amplification means fast P/E loss and low life.) Write amplification details and influencing factors For example, in the worst case, if I want to write a 4KB data, and the target block happens to have no free page area, GC recovery is required. Next, let's analyze the write amplification value of this process. First, the master reads the target block 512KB, then the GC recovers and erases 512KB, and then rewrites the 512KB blank area to store the original write 4KB data. That is, the original write data is only 4KB, and the actual write is 512KB, and the write amplification value is 512/4=128 times. Through the above examples, we should have a general understanding of the concept of write amplification and the harm of write amplification. So, what factors can affect write amplification? GC recovery mechanism, as shown in the example above, this mechanism requires the complete erasure of the entire block, thereby increasing the write amplification of the entire data. Wear leveling (WL), this mechanism mainly extends the overall service life by balancing all flash memory particles, but it still increases the overall write amplification. Trim mechanism, ATA instructions, avoid unnecessary GC recovery times, thereby reducing write amplification. In addition to the above-mentioned master control mechanism that can affect the value of write amplification, the size of the OP reserved space inside the solid-state drive also has a considerable impact on write amplification. The larger the OP reserved space, the more blank flash blocks are available. Even in the worst case (that is, all flash blocks are full), the master control does not need to perform GC recovery, which naturally greatly reduces the number of unnecessary reads and writes, thereby greatly reducing write amplification. After talking so much, some friends will definitely say, "What's the use of knowing write amplification? We can't prevent write amplification." In fact, for ordinary users like us, we can modify the OP reserved space and clean up useless data in the SSD in time to leave more blank space to reduce unnecessary erasing and writing, thereby reducing the write amplification value of the solid state drive and increasing the life of the solid state drive . More importantly, write amplification is the most critical factor in measuring the performance of a master controller. When purchasing a solid state drive, we can measure the master controller performance from the write amplification value to infer the overall performance of the solid state drive.As a winner of Toutiao's Qingyun Plan and Baijiahao's Bai+ Plan, the 2019 Baidu Digital Author of the Year, the Baijiahao's Most Popular Author in the Technology Field, the 2019 Sogou Technology and Culture Author, and the 2021 Baijiahao Quarterly Influential Creator, he has won many awards, including the 2013 Sohu Best Industry Media Person, the 2015 China New Media Entrepreneurship Competition Beijing Third Place, the 2015 Guangmang Experience Award, the 2015 China New Media Entrepreneurship Competition Finals Third Place, and the 2018 Baidu Dynamic Annual Powerful Celebrity. |
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