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Does file fragmentation in a USB flash drive affect the read/write speed of the flash drive or not
Fragmentation affects speed, but I think that's what mechanical hard disks used to be.

Nowadays, USB flash drives are electronic memories, so the effect is still there, but it should not be as big as a mechanical hard disk.

The following is my search for the owner of the U disk read and write speed information, you can refer to the following:

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We all know that the U disk is mainly composed of the main control chip and flash chip, so the factors affecting the speed of the U disk is divided into the main control chip and flash chip.

Baidu Experience:jingyan.baidu.com

Methods/Steps

1

First, the flash chip:

The flash chip has a lot of manufacturers, and there are a lot of models, so why is it that the same master control with different flash speed is not the same?

Flash has a direct impact on the read and write speed of several parameters:

serial access time, which indicates the flash transfer time of a byte of data (I/O transfer).

page read time, this is the preparation time needed before reading a page of data (flash to cache).

page program time, this is the time it takes to actually write the data to flash. (

2

Read and write of Flash chips are generally in the unit of page, the current size of a page of the latest flash is 4KB.

So the time to read a page is serial access time * page size + page read time.

The time to write a page is serial access time * page size + page program time.

3

Taking Samsung's 50nm SLC and MLC as a comparison:

serial access time is 25ns

page read time: SLC(25us) MLC(60us)

page program time: SLC(200us) MLC(800us)

So SLC reads a page in about 135us, which is equivalent to 29MB/s.

SLC writes a page in 310us. page is 310us, which is equivalent to 12MB/s.

And MLC reads a page in 170us, which is equivalent to 23MB/s.

MLC writes a page in 910us, which is equivalent to 4MB/s.

Seeing that MLC is much slower than SLC, especially the write speed.

These parameters don't vary much from manufacturer to manufacturer and model to model, so you don't have to pick and choose deliberately.

But the K9MDG08U5M (16GB) is an exception. Since SLC is so expensive, the rest of the analysis is based on MLC parameters.

4

The above is about the read and write speed of a single flash cell.

The so-called flash unit is not the chip that we see, the technical term is called plane.

In fact, it is a flash chip with multiple small pieces inside.

The size of a plane in the current MLC process is 1GB.

So a 4GB K9LBG08U0M has 4 planes.

A 8GB K9HCG08U0M has 8 planes.

5

Dual-channel is faster than single-channel, as we all understand. So if you can read and write to these multiple planes at the same time, the speed is multiplied.

While not at the same time, it is possible to alternate, that is, the serial access time can not be omitted, but the page read time and page program time can be **** enjoy.

The time to read a page to each of the 4 planes is 110*4+ 60 = 500us, 32MB/s.

The time to write a page to each of the 4 planes is 110*4+ 800 = 1240us, 15MB/s.

The time to read a page to each of the 8 planes is 110*8+ 60 = 500us.

The time to read a page to each of the 8 planes is 110*8+ 60 = 500us, 34MB/s.

The time to write a page to each of the 8 planes is 110*8+ 800 = 1640us, 19MB/s.

(Actually, it can be even faster, I won't go into details)

6

Nowadays, the newest flash provide such a features, then it's up to the host chip to use these features.

7

Then again, the master control:

The master control has a single-channel and a dual-channel, but it is not the ability to paste two pieces of flash is a dual-channel, dual-channel master control has two sets of independent flash I/O.

Dual-channel speed is simply twice as fast as a single channel.

The speed of each channel is mainly affected by how well the alternate read/write feature described earlier is done.

We also need to say a few words about the structure of the flash chip, the K9HCG08U1M, for example, the chip has two chip selection signals CE.

Each chip selection signal CE control a K9LBG08U0M (don't be surprised, the big flash is to take the small ones to put together).

Each K9LBG08U0M contains two DIEs (sorry, another flash architecture moniker),

and then one DIE contains the two planes mentioned earlier. so a K9HCG08U1M contains 2 CEs/4 DIEs/8 planes.

8

There is no need to alternate between CEs and DIEs. Doing the alternation between them is not the same as doing the alternation between DIEs and between planes, and the complexity is different.

Using only the alternation between CEs is equivalent to operating two planes.

Using the alternation between CEs and the alternation between DIEs is equivalent to operating four planes.

Using all of them is equivalent to operating eight planes.

This is the same as using the alternation between DIEs and CEs.

9

The oldest masters didn't even alternate between CEs, but nowadays the poorer ones probably only alternate between CEs, while the better ones do both.

We don't know how this is done for each master, but analyzing the speed, those with MLC double posting and large file write speeds greater than 20MB/s have done it.

10

Explain to everyone, originally according to the above algorithm, 8 plane parallel operation, coupled with dual-channel, read and write speed should not be 68MB/s and 38MB/s?

But USB is limited by the maximum packet size of 64KB under window, the speed limit itself can only reach read 32-35MB/s, write 28-32MB/s (approximate value).

The speed of USB in transferring data is indeed 60MB/s, but not all of it is valid data, and the valid data in a 64KB packet is about 5/6.

Worse still, it has to rest between two packets. So the flash side has to go up to 50MB/s to reach USB's top speed.

So the current limit of USB flash drive is probably read basically on 30MB/s. And write according to k9HCG08U1M double posting to see up to 25MB/s.

11

Finally, how do you choose the flash and the master to get the best speed?

(1) The larger the flash chip capacity, the more planes it contains, and the better the alternating reads and writes.

But K9MDG08U5M is not good, its serial access time is 50ns, twice as big as the smaller capacity ones.

(2) If you want to be fast, use dual-channel, and choose the one that does the alternating function well. Which masters are good? You have to measure it to know.