The USB capacity has reached 1TB, why it still can't replace SSD?

As flash storage products, the popularity of the USB drives predates the SSD. USB with smaller capacity have more acceptable price, which is the reason for the popularity of the USB early. But the capacity of USB drives has already reached the TB level now and the common capacity of SSDs is no more than that, why can USB not replace SSDs?

Difference between SSDs and USB drives in the principle and performance

1.The controller algorithm is different.
SSDs use a special algorithm that is encapsulated in the controller, which is different from each manufacturer. Through this special algorithm, data is evenly distributed on each flash in the SSD chip, which will increase speed and extend flash memory lifespan. Some manufacturers even use more efficient algorithms to read and write data compressed. Read speed can reach a high level and the lifespan of flash chip can greatly extend. In general, SSD have the lifespan of four or five years if used normally.

2. lifespan can be greatly extended
The reason why USB is often easy to be broken is that the general most of USB have only one flash memory and some high-end models contain at most two chips. Storage cell on the same chip is repeatedly read and written when chip is used, which will accelerate the aging of the chip and shorten the life of the chip. While SSD have dozens of chips rather than one piece of chip. Through the coordination of the controller, different data will be equally assigned to different chips to collaboratively operate. So, the times of chips reading and writing will increase and the time of stable work also are greatly prolonged.

The USB typically uses only 1-2 flash memory, up to two NAND flash chips, while the SSD has a larger number of flash memory which take advantage of concurrent reading and writing to gain greater efficiency. For a 1tb USB, the capacity of a single NAND flash requires a minimum of 512GB. If only one side can be welded, it requires a 1TB NAND flash. For SSD, take 1TB 850pro SSD for example, the following image you can see that it uses 8 NAND flash in total and the capacity of a single NAND flash is only 128GB. This single 128GB NAND flash process has been very mature and rate of good product is very high. While a single 512GB or even 1TB NAND flash are manufactured now, the rate of bad product is very high. So 1TB USB is more expensive than 1t SSD.

Under current 3D flash memory technology, it is not difficult to create a single flash with a capacity of up to 1 TB, but few manufacturers have applied such flash to SSD drives. High-capacity flash memory means fewer chips and less concurrent read and write.

3. USB is an external device of which the read speed is not faster than SSD
If you try to copy the same file to the USB drive and SSD, respectively, at a significantly faster speed than SSDs. The reason for removing the USB interface is also the reason for the internal FLASH chip principle structure. FLASH chip in the same memory cell structure, at the same time can only read or write this single operation. Mainly because flash chip to read and write data, is to rely on voltage changes to complete, read operation to a voltage, write operation to a voltage, and it is not possible to produce 2 kinds of voltage at the same time, but if there are many chips, the data is scattered, then for a chip combination at the same time read and write can be achieved.

In fact, the structure principles of SSDs and USB drives is the same, controller and flash chip. However, owing to size and cost，the controller of the USB is simplified and shrunk, it eliminates the sata controller, but retains universal controllers for computer mobile devices such as zif (ce), esata, usb. It is also said that the storage addressing capacity of USB is also simplified, the controller of USB support currently only a maximum of 8 flash chips. The controller of SSD typically supports at least 16 flash chips, some up to 32 flash chips or even more.
The USB drive is not as good as an SSD and its heat dissipation is not better than the mobile hard disk.

Of course, it's not always right to look at the number of flash chip, because a single flash particle can encapsulate multiple flash chips that are connected through very fine metal wires to communicate with the outside world through the pins of the package.

SSD controller is also far more complex than the USB drive, with more flash channels, and support more CE. So SSD have the handling capacity of a large amount of data at the same time

The following image shows a 512Gb Die of a Toshiba BiCS3 flash memory chip with two flash Plane.

In addition to the "flash channel", the flash die under the same channel has the ability to read and write in parallel between the plane flash faces in the same flash die.

Flash die achieves performance growth by interleaving read and write instructions

In addition to better performance, SSDs have better flash management capabilities, better error correction capabilities, and smart self-analysis and reporting capabilities to more accurately report remaining life expectancy. And the USB disk often uses low-quality flash memory chip, coupled with controller of which the error correction ability is low. So, it is easy to occur data loss, USB is not suitable for long-term storage data.

When the health state is reduced to a critical level, the TR200 can gave warning that the hard disk needs to be replaced through the toolbox software. If it is further used to the end of the flash life, TR200 also has read-only lock disk capability, which can switch to read-only mode in a critical situation, giving the user the opportunity to salvage data on the disk.

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