SSD: not all the same. What is right for you?
The last few years on the market of disk devices is a quiet war. On one side of the conflict are tested and available, but very old disk drives on hard magnetic disks that are part of the PC world for over half a century. With another lightning-fast new SSD drives, which rely on NAND chips flash memory.
For this reason, for most users, the choice of disk for a desktop or mobile computer comes down to the big question: HDD or SSD?
The advantages and disadvantages of each of these two standards we have already spoken. If you felt the temptation of the fantastic performance of modern SSDs, before you buy a specific model you will have to make another important choice.
On the market today, you can find three different main types of models depending on the specifics of NAND flash memory from which they are constructed: SLC, MLC and TLC.
What are the differences between them and why you should know it? Which type is best for you and your specific needs? All of these questions I will try to answer in this article.
Cells and bits
Total for three cuts – SLC, MLC and TLC is the principle that NAND memory is used to store information. The SSD consists of a number of flash chips and a special microprocessor controller, which controls the processes of writing and reading.
For this purpose he divides all available memory array conditionally on «cells», which records (and which reads out) information. There are also fundamental differences between the three types of NAND-memory. In each cell of the SLC memory (Single Level Cell) can store exactly one bit of information – zero or one. In MLC (Multi Level Cell) or two bits or more, and in TLC (Triple Level Cell) is three bits.
In theory it seems that the TLC technology is the most promising and the most potential of the three, but in reality everything is exactly the opposite. The reason for this has to do with the specific structure of the NAND chips used as the primary array to store information in a typical SSD. The problem is that the more write cycles passes the corresponding cell, the more it wears out. After a certain number of rewrites the information on the cell, it just stops working.
Between price and reliability
This is the main drawback of SSD technology compared with traditional hard drives. Magnetic disk also wears out over time, but it usually begins to give clear signs of this – there are bad sectors (i.e. parts which have become unfit for storage of information). Accordingly, this raises a number system alerts, which in many cases help to save at least part of the data stored on the «dying» disk and transfer it to other media.
Alas, but in the case of SSD, you can’t count on such warnings when their cells wear out, they just stop working, and the recorded data are vaporized in electronic oblivion.
Described the prospect sounds rather scary but do not panic – manufacturers SSD is very clear this lack of technology, so they took a number of precautions as to prevent the attainment of the worst-case scenario.
However, if you want to be as safe from the possible damage to the SSD and make him the greatest for a long period, be sure to pay special attention to the type of NAND chips, of which it is built.
The idea here is the following: as a rule, the most durable is the SLC-memory. It guarantees more than 100 000 write cycles, but is also the fastest of the three types of – time Erasure of a single cell in the range of 1 to 2.5 milliseconds.
Next in reliability are MLC chips. For them, the number of write cycles is estimated to range from 3000 to 15 000, and erase speed from 2.5 to 3.5 msec.
Is TLC memory from 1000 to 5000 write cycles and speed of 4 to 5 milliseconds.
What to choose?
Now you are probably thinking – so that everything is clear, we must take the SLC and everything will be fine. At the risk of suppress your enthusiasm, I must warn you that you will be very shocked when confronted with the prices of SSD devices based on SLC. For example, one relatively modest volume SLC-ROM production OCZ with a capacity of 60 GB (very few by modern standards) is… almost 35 000.
There are more expensive alternatives, however, as cheaper, but not many of them offered less than a 5-digit amount of money.
That’s why this class SSD devices designed for a specific range of systems, where a huge load (read and write) in conjunction with high requirements for security and reliability such as banking servers or other arrays for storing critical data such as archives of various government agencies.
If you have SLC drops out of the equation, then only MLC and TLC. The prices here much more reasonable and the selection of one of the two technologies comes down basically to answering the question «what specific purpose you will use your future SSD?»
As the number of «write cycles» is rather vague and difficult to understand for most ordinary users, here are some more digestible data. Tests show that with a daily load of about 20 GB (read / write) a typical TLC device on the 128 GB can provide uninterrupted operation of an average of 5-6 years is more than enough for any PC for General use (home or office system). When the same load MLC device promises a few years more, that literally borders on an eternity in the digital world.
Currently, the SSD models on the basis of TLC to provide the most reasonable balance between reliability, speed and price per Gigabyte. However, if you insist on a maximum level of security and are willing to overpay a little, then solid-state drives with flash memory MLC was right for you.
A nice compromise in this regard is the use of a MLC device with a small volume (60-120 GB) as the system drive. So your important files will be better protected and costs will remain within reasonable limits.
When possible purchase the SSD for other needs – for example, games (games readily takes a high speed of the disk), you can bet on TLC with more solid volume (256GB or more). So you will get the best price per Gigabyte of space, and in the case of a disk failure, the worst that can happen is to reinstall the operating system and your gaming collection.