Reading only wears out an SSD

SSD Lifetime: Answers to the Most Important Questions

Even if the service life of the storage cells of SSDs is limited, the positive news right at the beginning: Most solid state disks last much longer than the manufacturer specifies. Thanks to wear-leveling technology, the controller distributes the write access as evenly as possible to the billions of storage spaces and thus counteracts premature wear.

Nevertheless, it is a good idea to optimally set up the SSD and occasionally check its health. c't provides answers to the most important questions about extending the life of the SSD.

How many writes can an SSD take?

The flash memory cannot be overwritten as often as required; each individual cell can only withstand a certain number of write cycles. Most of the time, the data sheet tells you how much you can write to an SSD under the warranty conditions. For example, a Crucial BX200 with a capacity of 240 GB and a three-year guarantee period can handle 72 TB, i.e. around 65 GB per day. For comparison: on typical workstation PCs, the writing workload is between 20 and 30 GB per day. The writing load is only higher for users with all-day Photoshop or video editing sessions.

How are the size and lifespan of an SSD related?

If you have the budget, it is better to buy a slightly larger SSD than absolutely necessary. This not only prevents bottlenecks in storage space: the longer the number of flash cells, the longer the service life, because the controller can distribute the data better.

Which flash memory is particularly durable?

Flash cells differ in terms of their storage capacity. While a single level cell (SLC) can only store a single bit, a multi-level cell can store two bits and a triple level cell (TLC) three bits. SLC cells are particularly fast and durable. TLC cells store more information, but write more slowly and, with the same structure size, only reach a third of the life expectancy.

In general, the following applies: With increasing storage capacity of the cells and at the same time ever smaller structure widths, not only the production price per bit decreases, but also durability and speed.

Should you leave ten percent of the capacity of an SSD free?

It's a common myth: You should leave 10 percent of the capacity free so the SSD has more room for internal cleanup and increases its lifespan. However, this is not true: the SSD uses the unused memory anyway - whether it is assigned to a partition or not.

What do I have to consider when installing and setting up an SSD?

Windows version 7 or higher, MacOS and most Linux operating systems automatically recognize an SSD during installation or when moving from a hard drive. Windows automatically takes care of the deactivation of measures that accelerate access to conventional hard drives, but are unnecessary or even counterproductive for SSDs. However, there are still two important things to consider before and during the installation: The AHCI mode of the SATA controller and the Trim commandl.

There are some drives in older PCs that still work in IDE mode. This only allows one request at a time. Unlike hard drives, however, SSDs can process multiple requests almost simultaneously. To get more performance, you have to set up the BIOS setup appropriately: Switch to the AHCI mode of the SATA controller. This allows command queues with 32 requests. But be careful: If you switch a running system from IDE to AHCI, Windows often no longer boots - so it's better to set this before the installation. A subsequent change is also possible, either in safe mode or via the registry. How exactly this is funded is described in our hotline tip Change the polarity of Windows to AHCI.

Even if most operating systems automatically recognize SSDs, you should check for older SSDs whether the Trim command is supported. Only the trim command becomes active and the SSD also observes it, it can delete data that is no longer required in the background and make as many free data blocks as possible available. The TrimChec utility can be used to check whether the SSD supports the Trim command. TrimCheck writes a file, deletes it again and shortly afterwards checks whether the blocks previously occupied by the file are free again.

Are there any tools to check the health of an SSD?

The SSD can be continuously monitored with a tool for monitoring the SMART values. Even if an exit cannot be predicted specifically, the tools are useful. In addition to manufacturer software, there are universal tools such as CrystalDiskInfo, the Smartmontools from the Linux world and the Windows software GSmartControl based on it. However, with GSmartControl and Smartmontools you have to use your pocket calculator yourself if you want to know the amount of data written on the SSD. The tools only output the number of 512-byte blocks. This number has to be multiplied by 512 to get the number of KByte blocks written and divided twice by 1024 for the GByte specification.

Long-term monitoring is more convenient with the Hard Disk Sentinel: It logs the SMART values ​​in the background, generates line diagrams from them and, if desired, warns by sound or email when critical thresholds are reached.

What happens to the data if an SSD fails?

Most SSDs can no longer be accessed once they have been written to death. That means: Data stored on it are irretrievably lost and can no longer be read. The only protection against data loss is backups on another medium.

How do TLC and MLC SSDs perform in the long-term test?

Comparing the manufacturer's warranty with the actually achieved write performance - that was the mission of our SSD long-term test. The result of the tested SSDs was gratifying: All of them lasted significantly longer than the manufacturer promised. The Pro models from Samsung and SanDisk proved to be particularly durable.

How do cheap SSDs perform in the long-term test?

The cheap SSDs did better than expected in the c't long-term test. In terms of endurance, some of the tested cheap SSDs from Drevo, Goodram, Intenso, KingDian, Silicon Power and Teamgroup are even ahead of the established competition. You can read the entire test of cheap SSDs in c't 10/2017.

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