What are the real factors that affect solid state hard disk life

as TLC flash particles gradually occupy the market heights, the battle for the life of solid-state hard drives has again been put on the stage, arguing, just as the MLC became mainstream, as SLC continued to be weak. "See him on the high-rise, see him feast guests, see his house collapsed", everything is so, any new things replace the old things will go through a challenge to the process of repeated to accept.

Of course, today we are not going to discuss the SLC/MLC/TLC, but since we talked about the problem of solid life, in addition to the flash particle of its own physical fitness, in fact, the main control of the written amplification mechanism is also a key factor affecting solid life.

Write amplification mechanism

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

Write amplification, in English named Write amplification, which was first introduced and used in public submissions by Intel Corporation and Siliconsystems Corporation (2009 Western Digital Acquisition), at the earliest of 2008 years. This term describes actually a multiple relationship between the target write value and the actual written value of a solid-state hard disk, and the smaller the written amplification value, the higher the solid life expectancy.

To fully understand the write amplification, we need to first understand the solid-state hard disk reading and writing mechanism. We know that the solid-state hard disk storage unit is composed of flash particles, can not achieve physical data coverage, can only erase and then write, repeat the process.

As a result, we can imagine that, in the actual reading and writing process, the data can be read and written in the flash memory particles on a number of erase write, especially when some blocks have been completely stuffed.

These multiple operations, the increase in the number of writes and the number of original need to write the ratio, is called the write amplification. Therefore, the high number of written amplification, will be the loss of solid state hard disk life. (Solid-state HDD flash particles have a rated P/E value, that is, the maximum number of reads and writes, high P/E loss, low life expectancy. )

A detailed explanation of the written amplification and its influencing factors

For example, if I were to write a 4KB of data, and the target block had no free page area, GC recycle would be required.

Next, let's analyze the written amplification values for this process. First, the master reads the target block 512KB, then the GC reclaims the 512KB, and then overwrites the 512KB blank area to hold the original write 4KB data. That is, the original write data is only 4KB, the actual write to 512KB, write magnification value of 512/4=128 times.

As shown in the example above, we should have a general idea of the concept of write amplification and the hazards of writing amplification. So what factors can affect the write amplification? GC recycling mechanism, as the example above, this mechanism needs to completely erase the entire block, thereby increasing the entire data write amplification.

Wear balance (WL), this mechanism is mainly through the equalization of all flash particles, thereby prolonging the overall service life, but still increase the overall write amplification. The trim mechanism, ATA directives, avoids unnecessary GC collection times, thereby reducing the write magnification.

In addition to the above main control mechanism can affect the value of the written amplification, the size of the OP reservation inside the SSD has a considerable effect on the write amplification. The greater the OP reservation space, the more blank flash memory available, even in the worst case (that is, all flash blocks are full), the master also eliminates the need for GC recovery, and naturally greatly reduces the number of redundant reads and writes, thereby greatly reducing the write amplification.

Talk so much, certainly have a friend will say, "know to write amplification, what is the use?" We can't stop the write amplification. ”

In fact, for our ordinary users, we can modify the OP reserve space, as well as in time to clean up the useless data in the SSD, to allow more space to reduce redundant erasure and write, thereby reducing the solid-state write amplification, improve the solid life.

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 measuring the master performance from the write amplification value when buying a solid-state drive.