What is SSD disks and how they work?

Что такое SSD диски и принцип их работы

Today, we will discuss the main points and principles of the operation of solid state SSD technology. As you remember, in the first part of the article we conducted comparative testing of one SSD and two HDD disks. Considered how it looks from the inside and from which main blocks it consists.

Also - listed the main advantages of this technology, and now consider the shortcomings that are inherent in it at the moment. Let's present the main ones in the form of a list:

  1. High (relative to HDD drives) cost of data storage, i.e. - we get less disk capacity for a lot of money
  2. The greater vulnerability (with respect to devices with a magnetic recording principle) to electrical interference and power supply problems (sudden power outages, magnetic fields, static electricity)
  3. You can not completely fill the disk (15-20% of the space should be free)
  4. The lifetime of the media is limited to a certain number of recording cycles of its cells

But let's - in order! To begin with, what is a SSD drive and what is the principle of its operation?

SSD drive SSD drive

It is a solid-state drive in which chips of NAND flash memory are used instead of traditional plates of hard disks covered with a ferromagnetic layer.

NAND Memory Chips NAND Memory Chips

NAND memory is an evolution of flash memory, the chips of which had much less performance, longevity and constructively looked more massive.

Perhaps you will be interested in that the flash memory was developed in one of the divisions of the company "Toshiba" in 1984. The first commercial chip based on this development in 1988 was released by Intel. And a year later (in 1989) the same "Toshiba" introduced a new type of flash memory - NAND.

At the moment there are three main versions (modifications) of NAND memory:

  • SLC (Single-Level - Single Level Cell)
  • MLC (two-level - Multi Level Cell)
  • TLC (Three-Level - Three Level Cell)

The most expensive and reliable solutions are devices on SLC chips. Why? They allow only one bit of information to be stored in each memory cell. Unlike them, MLC and TLC chips can store two and three bits respectively. This became possible due to the use of different levels of electric charge on the gates of memory cells.

Schematically, it can be represented like this:

Such a multilevel structure allows dramatically increase the capacity of chips with the same physical volume (in the end, each gigabyte is cheaper). BUT! Nothing is given for free! Therefore, MLC and TLC chips dramatically shorten their "life", which is directly related to the number of cycles of overwriting their cells.

For the SLC, this is 100,000 erase / write cycles, for the MLC 10,000, and for the TLC, only 5,000. This decrease in reliability is due to the gradual destruction of the dielectric layer of the floating gate of the cell due to a small reserve of its state change due to electric current. Plus, due to the fact that with every new level the task of error-free recognition of the level of an electrical signal becomes complicated, which means that the total time of searching for the desired cell with data increases, the probability of reading errors increases.

In order to combat the phenomena described above, manufacturers have to develop specialized highly intelligent control microcontrollers for SSD disks that, in addition to input-output procedures, must write information to the media so that the chips of its flash memory wear evenly and control this wear, balancing the load, also - carry out error correction, etc.

It is the controller that is the weak point of solid-state SSDs, since it is more sensitive to power problems and damage to the firmware (firmware) contained in it, can lead to a complete loss of all user data. And their correct recovery is an even more labor-intensive operation than in the case of HDD disks. Due to the fact that the data is scattered across different memory chips and it is necessary to restore correctly their original structure, and this is not easy.

Therefore, manufacturers of SSD drives regularly update the firmware of their disks and upload them for free download, improving and improving the algorithms of the device and preventing the loss of data in the event of an emergency.

Recommendation! Periodically update the "firmware" of your SSD, downloading it from the manufacturer's website.

With the deterioration of MLC memory cells, manufacturers are also struggling with a method well established in magnetic recording discs: reserving part of their volume (10-20%) for the dynamic replacement of worn out cells. In the case of HDD, this area serves to replace the bad sectors of the hard drive.

But we, as users, can help our SSD drive in the idle not to waste its limited "life" resource and configure the operating system in such a way as to minimize unnecessary disk accesses.

I will show the general principles of what to do and what to avoid, and you will already set up your system for optimal work with a solid-state drive.

For example: we know that the operating system "Windows" during its work actively uses the swap file (hidden system file "pagefile.sys"). What does this mean, with respect to the deterioration of SSD drive cells and all of what we mentioned above? And the fact that a separate area of ​​the system flash drive is intensively used (it is often overwritten by some official and not needed data and, in fact, it is actively worn out)!

What can be done? Correctly! Transfer the swap file to another (not an SSD drive), as I did, or, with a large amount of RAM , completely abandon it (put it in "0")?

We go further: the defragmentation procedure is not only not necessary for this type of device (access speed for them is the same for any cell, regardless of where the final file is), but it is simply harmful. For the same reason as described above. Excess (idle) access to the disk only further reduces its limited resource. So - turn off the corresponding defragmentation service. Also, it is not superfluous to disable the indexing of files, which is necessary for faster searching, but is it often used by us?

The principle, I think, you caught. And now I would like to show you a small program "SSD Mini Tweaker" (tweaker-optimizer), which similarly optimizes the operation of the SSD drive. It is enough to put the necessary checkboxes in front of the corresponding items and click the "Apply Changes" button.

The computer will reboot and the changes take effect. The program is remarkable in that it has a Russian interface and detailed information in Russian. So, at any time you can get acquainted with the function that you are going to disconnect or keep involved.

Download the utility from our website. In the archive - versions for 32-bit and 64-bit systems and a help file in Russian.

Since we have devoted so much time to the optimal use of the disc and the wear and tear of its memory cells, I can not fail to present you another interesting development. The program "SSD Life Pro", the main task of which is to keep track of the disk's operating time and to report the approximate date of its failure.

Unfortunately, the utility could not calculate the "lifetime" of my disk "Plextor", but showed some other interesting information.

What do we see here? The entry "FW: 1.00" is the firmware version of the disk, below shows the occupied and free space on it, the total operating time from the first power-up and the number of starts. Also note the TRIM line (should be active), this indicates that the performance of the SSD drive will be optimal.

Below is a screenshot of the work of the same program, but taken from the site of its developer. It shows that the drive from the company "Intel" correctly transferred the utility of its SMART parameters and based on them the utility displayed an extended forecast of its state.

As you can see, the drive failure is "appointed" on November 7, 2020 :)

If we click on the link "How do you think this?" At the top of the program window, then go to the developer's site and we will be able to see (in Russian) how exactly this calculation is made?

At the conclusion of this topic, we will listen to the recommendation of all respected Intel firm, which says that the ideal operating conditions for a solid-state drive SSD is its data coverage by less than 75%, with a static (rarely changed) and dynamic (often changing) information ratio of 3 to 1. Do not use the last 10-20% of the disk space, as they are necessary for the correct operation of the "TRIM" command. To work it needs free space to regroup the data (the same as for the defragmentation function). The general rule is that - the more free space - the faster the device works.

At the moment, the SSD drive is ideally suited as a system partition on which the operating system and programs are installed and - everything. The data and all work on them should (if possible) take place on the second (HDD) disk. Also, solid-state disks can be effectively used on servers for caching static data.

And now, let's briefly consider why the more expensive SSD models of solid-state drives have such excellent high-speed qualities and what is still different from their "younger" brethren?

Firstly: it is the same smart drive controller chip that can be designed as a multi-channel one. - can write data simultaneously to each chip of flash memory disk. As a result, the overall performance of the device will be equal to the speed of a single memory chip multiplied by the number of channels of the controller. Well, it's a bit simplifying the situation :)

Also in more expensive models additional elements are used which are soldered to the board. This can be, for example, a series of capacitors located near the disk's RAM chip, which ensure guaranteed storage of data from the cache in the event of a power failure.

When the critical mass of bad cells of the drive reaches the critical level, the firmware of the chip can completely block the SSD drive for the write functions and put it into the "read only" mode, which guarantees the safety of the user's data (the ability to backup data) until the device completely fails.

And at the end of this article, let's touch on another interesting version of solid-state drives. This is "RAM SSD" drives. What is it?

Such hybrid devices use for information storage volatile chips, completely identical to those used in the modules of the computer's RAM. They have ultra-fast data access speed, read and write speed, and can be successfully used to speed up large databases and where peak performance is required.

Such systems are equipped with batteries to maintain operation in the absence of electricity, and more expensive models - backup systems, when data is copied to the HDD carrier.

This is how a similar device, which is defined by the operating system as a hard disk, can look like.

RAM SSD drive RAM SSD drive

And here is a simpler version, made in the form of a PCI Express X1 card

As you can see, the principle of operation here is the same, but the function of RAM chips or "pancakes" of HDD is performed here by usual RAM modules.

Now, as promised, I want to say a few words about subjective sensations after using a solid-state drive. The operating system (Windows 7) is loaded and turned off much more quickly. The same can be said about installing and running programs. Some applications simply surprise: "Microsoft Word 2003" "shoots" less than a second! You do not have time to mentally prepare for work with him :) Yes, quickly, but do not expect something phenomenal, all the same it's not a "revolution", but an "evolution" :)

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