True factors affecting SSD life: Write Amplification

As TLC flash particles gradually occupy the market heights, the life of the solid-state drive is once again on the stage, arguing that, as with the same year SLC constantly weak, MLC became mainstream. Really "see him on the high-rise, seeing him feast guests, see his building collapsed", everything is so, any new things to replace the old things will go through a challenge to the repeated to accept the process.

Of course, today we are not to discuss the question of the merits of SLC/MLC/TLC, but since the talk about the solid life of the problem, in addition to the flash particles of their own physique of the deterministic role, in fact, the main control of the existence of the amplification mechanism is also the key factors affecting the solid life.

Write amplification mechanism

So what is the write amplification mechanism? How does write amplification affect solid life? Then I'll talk to you about writing amplification.

Write amplification, the English name is write amplification, the term was first in about 2008 years, by Intel Corporation and Siliconsystems Company (Western Digital Acquisition in 2009) was firstly presented and used in public manuscripts, This term describes in fact a multiple relationship between the target write value of the SSD and the actual write value, and the smaller the write amplification value, the more the solid life can be improved.

To fully understand the write amplification, we need to understand the SSD's read-write mechanism first. We know that the SSD storage unit is composed of flash particles, can not achieve physical data coverage, can only erase and then write, repeat the process .

Thus, we can imagine that in the actual reading and writing process, the data read and write is bound to the flash particles on a number of erase writes, especially when some chunks have been completely stuffed.

These multiple operations, the increase in the number of writes and the original number of writes required, is the ratio of the so-called write amplification. Therefore, the write amplification value is high, will lose the solid-state drive life. (Solid-state drive flash particles have a rated P/E value, that is, the maximum read and write times, write amplification high, P/E loss fast, low life.) )

Write amplification details and influencing factors

For example, in the worst case, if I were to write a 4KB data, and the target block did not have a free page area, GC recycling would be required.

Next, let's analyze the value of the write amplification for this process. First, the master reads the target block 512KB, then the GC recycles erase 512KB, and then overwrites the 512KB white space to hold the original write 4KB data. That is, the original write data is only 4KB, the actual write 512KB, write amplification value of 512/4=128 times.

From the above example, we should have a general understanding of the concept of write amplification, as well as the harm of writing amplification. So, what factors can affect write amplification? The GC recovery mechanism, as shown in the example above, requires a complete erase of the entire chunk, which increases the write amplification of the entire data.

Wear leveling (WL), which is mainly achieved by balancing all the flash particles, thus prolonging the overall service life, but still increasing the overall write amplification. The trim mechanism, ATA instructions, avoids unnecessary GC recoveries, thus reducing write amplification.

In addition to the above-mentioned master mechanism can affect the value of the write amplification, the SSD internal OP reserve space size for write amplification also has a considerable impact. The larger the OP reserve space, the more blank flash blocks available, and even in the worst case (that is, all the flash blocks are stuffed), the master does not need GC reclamation, which naturally greatly reduces the number of reads and writes, greatly reducing write amplification.

Having talked so much, surely a friend would say, "What's the use of writing amplification?" We cannot prevent write amplification. ”

in fact, for our average user, we can reduce the write amplification value of the solid state and improve the solid life by modifying the OP space and cleaning up the unused data in the SSD, leaving more white space to reduce unnecessary erasure and write .

More importantly, write amplification is the most critical factor in measuring a master performance, and we can infer the overall performance of a solid state drive by writing amplification values to measure the master performance when choosing a SSD.

True factors affecting SSD life: Write Amplification