Solid state drives or SSDs have quietly become a revolution for the world of PCs and laptops , but they have done so with some hesitation.
One of the most frequent is that urban legend that seems to point out that the useful life of these units is not as good as that of a traditional hard drive. As we will soon discover, the most likely is just the opposite , and it is all due to the evolution of a technology that manufacturers in fact mark us with pessimistic reliability … just in case.
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The price of SSDs has dropped dramatically in recent times, and both SATA and M.2 NVMe models are now within reach .
The performance of these units has proven to surpass traditional hard drives on all fronts except the gross capacity : if we need several TB available, the obvious choice is still HDDs.
But except for that factor, SSDs have become the clear choice, among other things due to their own operating principle .
The NAND flash memories used are much faster than hard drives in both reading and writing, although in its design it must be borne in mind that these cells can be programmed and deleted (P / E) a limited number of times . This description is important because when data is written (“programmed”) to a NAND cell, the previous data must be deleted before it can be saved in the destination cell.
Although so-called P / E cycles are an important way to measure the reliability of SSD drives, there are actually other factors that affect those life cycles. Let’s see the three most important :
- P / E Cycles : When writing to an SSD the data is written and then erased to be rewritten. The number of P / E cycles that SSDs support is highly variable, and typically ranges from 500 to 100,000.
- TBW : This magnitude, which stands for “TeraBytes Written” indicates the total number of data that can be written to an SSD before it begins to fail. In a unit like the Samsung 970 EVO, it is indicated how, for example, 150 TBW are estimated for 250 GB models, 300 TBW for 500 GB models, 600 TBW for the 1 TB model and 1,200 TBW for the 2 TB model. These units are warranted for 5 years or the specified TBW, whichever comes first.
- MTBF : (or Mean Time Between Failures) is the reliability measure that normally indicates how many hours pass before a drive failure can occur. On a hard drive the MTBF is usually around 300,000 hours, while on an SSD that MTBF is normally 1.5 million hours. It is not the time the drive can last, but the average time we can wait before a drive failure occurs.
These magnitudes help to understand how reliable a unit is, and probably the clearest for users is that TBW that reveals the enormous amount of data that we should write before the unit degrades.
If for example we think about that data of 150 TBW for a 250 GB drive, we would have to write more than 80 GB a day for a whole year to reach those limits that Samsung talks about, an amount that rarely occurs in conventional users .
The normal thing, in fact, is that these units reach a useful life well above the specifications set by the manufacturer, since the tests and data carried out by these manufacturers are practically pessimistic cases .