With what seems like a very sudden move, SSD technology has gone mainstream. These fast solid state drives are common even in mid-range computers. Even the next generation Playstation will have an SSD instead of the more traditional hard drive.
Overall, this is good. Solid state drives represent a significant leap in performance over traditional hard drives. However, they also bring with them some special considerations for use and maintenance. Most users reading this probably already have an SSD on their system, or will almost certainly get one on their next system.
So, now is the time to uncover one of the most important but misunderstood issues unique to SSD technology. We’re talking about SSD wear. The mythical drive killer that kept many early adopters of this technology awake at night.
Before we can decide what SSD wear actually is, we need to briefly discuss how SSDs differ from the hard drives we all know and love.
How Solid State Drives and Traditional Hard Drives Differ
How do SSDs and traditional hard drives differ
A traditional mechanical hard disk consists of platters coated with a special magnetic material. The platform spins at thousands of revolutions per minute, while the read / write heads slide across their surface in an air pocket thinner than a human hair.
The first hard drives were so large that they needed an airplane to deliver – and they only contained a few megabytes of data. A 4TB portable hard drive fits easily in your pocket these days. These drives are cheap, roomy, and quite reliable compared to how they were originally.
However, mechanical hard disk technology cannot keep pace with the development of solid state computer components such as processors, RAM, and flash memory. Plates can only rotate so quickly, read / write heads can only move when the laws of physics allow objects with such a large mass.
Solid state drives have no moving parts. It’s all about the semiconductor circuit. Electrons can travel through silicon chips much, much faster than any mechanical component could. This is why even the cheapest SSD will completely ruin mechanical drive performance.
Since they have no mechanical parts, they are much less fragile physically and less prone to breakage. On the other hand, simply using an SSD will shorten its lifespan, and if you use them incorrectly, that reduction can be quite significant. So what’s going on?
Why do SSDs wear out?
Why do SSDs wear out?
First, reading data from an SSD has no discernible effect on its lifespan. Instead, it is the process of writing to a flash memory cell that degrades it. Every memory cell in an SSD has an oxide component. Two layers of one or another chemical mixed with oxygen. Electrons are trapped between these oxide layers.
The state of this cell depends on the charge level. In other words, how many electrons are trapped between oxide layers. Each time this state changes, the oxide layers wear out, eventually losing the ability to hold electrons. This can make the state impossible to read correctly. Write to the cell too many times and it will eventually go bad.
Solid State Drive Technology Types and Lifetime
Types of SSD technology and endurance
While all SSDs suffer from write wear and tear, not all are equally resistant to it. There are various designs of memory cells that change the amount of information that can be stored in one cell.
The most robust design is known as SLC or sibling memory . In this case, only one bit of data is stored in the cell, which makes them binary. Thus, it is quite easy to distinguish the level of charge corresponding to a particular state, even after significant wear.
MLC and TLC layered and three-level circuits store two and three bits per cell, respectively. Their cells have multiple levels and therefore many different states that need to be read. Since the boundaries between the different states of the cells are narrower, even a little wear and tear can cause problems with the electronic capacity, making it impossible to remember the correct state.
So we should only use SLC, right? The problem is that SLC is incredibly expensive per gigabyte. It is fast and durable, but not very dense. Most modern premium SSDs in computers use MLC, and TLC is becoming more popular for its higher capacity at a good price.
So how worried should you be that these cheaper products don’t work in practice?
Practical SSD Endurance
SSD endurance in practice
The answer to this question today is “quite a bit.” In the early days of computer SSDs, you could destroy one in just a few hours, clogging it with write requests. Today, multi-layered discs can be expected to have much greater write endurance than the average user would ever need.
There are several reasons for this, but it all comes down to the fact that the drives themselves are much smarter and modern operating systems know how to properly use SSD drives.
For example, solid state drives now use a technique known as wear leveling. This transparently spreads the write to the cell across the entire disk so that wear and tear occurs evenly. Otherwise, some cells would die much faster than others.
So how much record endurance can you expect? Latest generation drives such as the Samsung 950 Pro 512GB have 400TB recording capacity. However, many people still use popular older drives like the 850 EVO This drive is rated for “only” 150 TB.
Torture tests show that this is a very conservative rating. In real life, this drive model required a whopping 9100 TB of write operations before getting rid of the ghost. Thus, the number of 150 TB is just the moment when the manufacturer will no longer honor the warranty.
However, consumer-grade drives should not be used for any task where there are many writes to the disk all the time. They are not suitable for use on a server or as scratch discs with heavy media. However, for normal day-to-day consumer use, writing permanence is something you never have to spend time thinking about.
Buy a good brand of disc and back up your critical data regularly anyway.