As a non-volatile storage medium, NAND flash memory has become a better storage device than hard disk drives due to its low power consumption, light weight, good performance and ability to retain data even after power outage, making it very suitable for portable devices. memory to use.
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Solid State Disk (SSD for short) is a storage product based on NAND flash memory media. In recent years, due to the advantages of low power consumption, high performance, stability and security of SSD, it has become more and more popular among customers, and SSD has gradually been widely used in IT operation and maintenance, finance and other industries. |
Performance vs. cost, how can SSD have both?
A NAND flash memory chip encapsulates several DIEs (or LUNs). Due to the development of NAND flash memory media technology, the number of layers is constantly increasing, and the capacity of a single DIE is also increasing. For an SSD of the same capacity, the number of DIEs required is The number will decrease accordingly. The benefit is that the cost and price per unit capacity of SSDs continue to decrease, which not only benefits users, but also helps expand the scope of use of SSDs. But at the same time, the reduction in the number of DIEs will lead to a reduction in NAND read concurrency, and the read performance will also be reduced. In the face of users' increasing performance requirements, this shortcoming will limit the expansion of SSD usage.
In layman's terms, SSD can be understood as a community that needs to accommodate a certain number of residents. NAND flash memory chips are equivalent to one of the communities, DIE is equivalent to the buildings in this community, and Plane can be understood as each floor of this building. Portal, each Plane is divided into many Blocks, Block is equivalent to the number of rooms in each household, Page is equivalent to the number of people in a room (Block), and the concurrency can be understood as the number of people in the building. Elevators, due to bus restrictions, can only carry one person at a time. Due to the development of construction technology, each building (DIE) can be built from the original 8 floors to 16 floors. That is, each building can accommodate twice as many residents as before. Under the condition of a certain number of residents (the same capacity) SSD), the number of buildings (DIE) can be reduced by half, land and construction costs are reduced, and housing prices will be relatively cheaper, so it will be welcomed by home buyers. However, since there is only one elevator (concurrency) in each building (DIE), the number of elevators is also reduced by half as the number of buildings decreases. For residents, the travel efficiency is greatly reduced, which will inhibit the purchase intention of home buyers. .
In order to reduce the impact of this problem, SSD manufacturers have proposed solutions such as increasing the operating frequency of the elevator to speed up the transmission rate of the elevator, or having the building management notify people on the same floor that they are ready to go out and queue up at the elevator entrance to take the elevator. .
Currently, SSDs basically adopt a Multi-plane (multi-plane) design (the mainstream uses a 4-plane design, which is equivalent to 4 households on a floor, and 4 households share an elevator, that is, "one elevator, four households"). With the development of technology, the reading method has evolved from Single-plane read to Multi-plane read, that is, from the beginning, only 1 person in a room in one household can be notified at a time. One person prepares to go out and then takes the elevator, which develops into four people in four rooms on the same floor preparing to go out and queuing up to take the elevator.
This technology has greatly improved the performance of sequential reading, but the improvement of random reading performance is mediocre, because when reading sequentially, it is like the building manager taking the elevator in sequence to each floor to notify residents to prepare to go out, and every time people on the same floor You can prepare to go out at the same time, which greatly shortens the time to prepare to go out; but when reading randomly, it is equivalent to the building management having to go to different floors to notify people in the designated portal rooms to go out, and only those who are ready first can ride first, and so on. Only when the person in front has finished riding can the people on other floors be allowed to ride. This is not much different from the Single-plane pronunciation.
In order to improve random read performance under the premise of high sequential read performance, the Asynchronous Independent Plane Read (AIPR) function came into being.
The AIPR function is designed to improve random read IOPS. During random reading, the AIPR function can increase concurrency and improve the utilization of the data transmission bus, thereby improving random read performance. That is to increase the number of elevators in the building and install a dedicated elevator at the door of each row of households. Although due to Bus restrictions, only one elevator can be used in the building at the same time, the building management can notify the people on a floor. After preparing to travel, immediately take the elevator to notify other residents on the other floor that they are ready to go out. The preparation time for each row of residents to go out is parallel. Once ready, you can take the elevator at the door, which improves the utilization rate of elevator transmission and thus improves travel. efficiency.
The following section introduces the advantages of AIPR by introducing the evolution and comparison of the above three reading methods:
1、Single-plane read
Single-plane read, that is, only reading the position in one plane at a time. The schematic diagram is shown in Figure 1 below for Single-plane read. Taking the 4-plane TLC block as an example (the same below), because DIE is the unit of concurrency, due to the existence of tR (read operation time), it takes 4 tR times to read 4 planes at this time, all read operations and data transmission Serial, longer read latency and lower performance. To relax this restriction, Multi-plane read was introduced.
2、Multi-plane read
Multi-plane read, that is, the position in multiple planes can be read at the same time, as shown in Figure 2 below Multi-plane read. For Multi-plane read, the read operations of all planes start at the same time, and the read position requirements in each plane are the same. Although DIE is still used as the concurrency unit, compared with Single-plane read, this method has parallel read operation times, which greatly shortens the read latency and improves the sequential read performance.
This method is very effective for improving the speed of sequential reading, but for random reading, Multi-plane read is almost the same as Single-plane read. Now, in order to further improve random read performance, it is proposed to change the concurrency unit from DIE to plane, and the AIPR function is introduced.
3. AIPR
After the AIPR function is turned on, the timing and position of read operations on different planes are completely independent, that is, different planes can perform asynchronous and independent operations (AIPR in Figure 1 or Figure 2). Through AIPR, the read operation of each plane can be started independently. Data out command can also be started independently after the read operation of each plane is completed.
When performing random reading, the concurrency of AIPR is 4 times that of Single-plane read (taking 4-plane as an example), and when performing data transmission, the data transmission bus utilization rate of AIPR method is higher, which is suitable for random reading of small-capacity disks. The read performance improvement is more obvious. As shown in Figure 1, it can be found that the AIPR function has obvious performance advantages.
Figure 1: Comparison of random read Single-plane read and AIPR
When performing sequential reading, compared with Multi-plane read, the data transmission bus utilization rate of AIPR method will be higher and it also has certain performance advantages, as shown in Figure 2.
Figure 2: Comparison between sequential read Multi-plane read and AIPR
With the rapid development of 3D NAND flash memory, the number of layers and density of NAND media are getting higher and higher, and the capacity of a single DIE is also increasing. When the total disk capacity is fixed, the number of DIEs will decrease. If you still read and write according to the Single-plane read and Multi-plane read methods, the total concurrency of the disk will also be reduced accordingly, resulting in reduced performance. Compared with Single-plane read and Multi-plane read, AIPR improves the utilization of the data transmission bus by increasing concurrency, thereby improving random read performance, and the random read performance of small-capacity disks is significantly improved.
A new generation of SSD high-speed storage media based on the storage-as-a-platform strategy
Inspur NS8500G2/NS8600G2, which uses AIPR technology, is a high-performance enterprise-class solid-state drive. It uses PCIe Gen4.0 Performance: Sequential read performance reaches more than 7000 MB/s; 4K random read IOPS can reach more than 1600K, which is improved to 3.6 times that of Single-plane read/Multi-plane read mode. The new generation of SSD high-speed storage media is available in single-port and dual-port forms. It supports full-path end-to-end protection and domestic and foreign encryption algorithms, making data more durable and reliable. Through multi-level fine power consumption adjustment, the energy consumption ratio is increased by 37%. It is widely used in cloud storage, database, artificial intelligence, big data, Internet of Things and other fields, ensuring data security for more than 700 customers in finance, communications, Internet and other industries, so that data will never be lost.
In recent years, Inspur Information Storage has continued to increase investment in technology research and development and product innovation, constantly absorbing cutting-edge technologies from various ecological industries, and unremittingly pursues the concept of lean manufacturing to provide customers with a more extreme performance experience, giving full play to the high efficiency and high efficiency of NAND flash memory. With the advantages of reliability and greenness, we use innovation to promote technology productization, fully release the value of data, and accelerate the digital transformation of various industries.