external ssd An article to learn about solidstate drives (SSDs)

external ssd An article to learn about solidstate drives (SSDs)

external ssd An article to learn about solidstate drives (SSDs)

disco SSD SSD OEM external ssd solid state diskexternal ssd, SSD SSDs are hard disks made of solid-state electronic array of memory chips external ssd, mainly consists of two parts: (Note: This article mainly introduces mainstream products)

1 Master unit: used to operate the storage unit, and resides a certain firmware, with parts of the operating system.

2 Storage array: Flash memory chip (NAND FLASH), single-chip FLASH chip has 64GB/128GB/256GB, and a small number of SSD memory chips are made of DRAM chips.

the appearance of the SSD can be made into a variety of shapes, for example: notebook hard disk, micro hard disk, Memory cards, U disks. The biggest advantage of this SSD is that it can be moved, and the data protection is not subject to power control, can be adapted to a variety of environments, suitable for individual users.

common SSD internals are shown in the following figure, which is mainly composed of a controller, power supply, NAND FLASH array, and external connectors.

external ssd
external ssd

the external interface mainly protects the following: IDE, SATA, mSATA, PCI-E, M.2, IDE interface of the SSD due to the use of parallel data transmission mode, more data lines, and often slower speed has been gradually eliminated; SATA2.0 supports the maximum rate of 3Gbps, such interfaces due to the maximum support of the limited speed, can not fully play the performance of the SSD. SATA 3.0 supports a maximum speed of 6Gbps (Gb per second). The biggest advantage is that the current market is very mature, and many hard disks on the market are such interfaces.

mSATA, also known as mini-SATA, is suitable for occasions with high dimensional requirements, mSATA is a miniaturized SATA interface.

PCI-E interface is also the initial emergence of an interface, began to be mainly used in enterprise SSDs and other data transmission occasions, with the arrival of SATA interface rate bottleneck, PCI-E hard disk gradually began to become popular in the high-end consumer market.

M.2, formerly known as the NGFF interface, is a new generation of interface standard tailored for super notebooks, mainly used to replace the mSATA interface. Whether it is in terms of very small size or transmission performance, this interface is much better than the mSATA interface. M.2 can support both SATA and PCIE interfaces, today’s M.2 interface can support PCI-E 3.0 x4 channels, the theoretical bandwidth reached 32Gbps, and the interface supports the new NVME standard, further improving the data transfer performance of SSDs.

SSDs usually contain multiple FLASH chips, each flash can be divided into multiple Planets, and each Plan can be divided into multiple blocks. Usually use 2D NAND FLASH, the latest development of 3D NAND FLASH has been interviewed, the use of stereoscopic stacking can make the capacity of single-chip NAND FLASH greatly improved.

Block is what we usually call a block, which reads and writes data to a block. On each block, it can be divided into multiple Pages, and the single Page of the vast majority of SSDs consists of a 4Kb data area + 128b OOB.

OOB (out of band, out of band) is an additional data space in NAND Flash for additional ECC error correction codes and metadata.

Page is the smallest unit during data reading and writing, that is, only the entire Page can be operated on when writing data and deleting data. So When Nand Flash is designed in hardware, for each piece (Plane), there is a corresponding area dedicated to storing cache data, and the data to be written to the physical storage unit or just read out of the storage unit is put into this data buffer, which is essentially a cache buffer, also known as page register. The data flow direction of the SSD when reading and writing data is as follows.

What are the storage particles?

storage particles are the smallest units for storing data, and there are currently three main types: SLC, MLC and TLC.

particles are all life-bearing, that is, the SSD has a life, after reaching the life of the SSD, the number of bad blocks inside the FLASH will rise exponentially, and soon the hard disk cannot be used. The factor that directly affects the life is the number of repeated erases of the storage particles.

where: SLC is 30,000~100,000 times; MLC is 3000~5000 times; TLC is 500 to 1000 times. The mainstream SSDs on the market are all TLC granules, with large capacity and low prices. In the occasion of high reliability requirements, MLC particles can be used, SLC is usually used in high reliability occasions such as national defense and military industry, usually the FLASH price of single-chip 64GB SLC particles can reach several thousand yuan.

all the information in the computer is returned to 0 and 1, so any object that can be used to distinguish between 0 and 1 can be used to record data, such as the original way of counting with knots in a rope.

write data, a voltage is applied to the CONTROL and some of the electrons are transitioned to the FLORATING layer when the electrons flow through the DRIN from SOURCE.

erased, the semiconductor at the bottom of the voltage, you can release the electrons in the suspension layer, in the absence of an external electric field, the electrons in the suspension layer due to the action of the upper and lower Two SiO2 layers can not escape, the charge / data can be stored for more than ten years.

this single particle only high or low two states of particles is the SLC mode of operation, because in the process of continuous scribing, the electrons need to constantly cross the middle SiO2 substrate, will gradually destroy its ability to isolate electrons through, until the particles are completely damaged.

SLC single particle has two levels, can save 1 bit of data, MLC can save 2 bit of data, TLC can save 3 bit of data, QLC can save 4 bit of data, but because of its life is only more than a hundred times, it is rare to see this product on the market.

the life protection mechanism of SSDs: the number of erases and writes is not enough, and the capacity is made up.

1 capacity redundancy operation: Why did we buy a 512GB hard disk with only more than four hundred GIBs in hand, in addition to the firmware used to store the SSD itself, there is a large part for backup, when a Page particle is broken, mark it as unavailable, and replace it with a spare area.

2 Write data equalization operation: If you repeatedly write 4KB of data to an SSD with A TLC particle 1000 times, will the disk break? The answer is of course no, the controller will automatically assign the physical address of the flash unit, and will try to avoid repeated reading and writing to the same BLOCK for a long time, so as not to affect the life.

there are many other protection operations, welcome to leave a message to communicate and discussdisco SSDSSD OEMexternal ssd