There’s a common belief that SSDs last much longer than HDDs. The reason being that they have no moving parts while HDDs rely on disk platters which constantly spin at speeds of 5400-7200 rpm. As such, sudden jerks or falls can damage them, causing a system crash or loss of data.
In HDDs, tracks are the building blocks of the storage memory. In SSDs, that same functionality is provided by cells. A cell is essentially a Gate Circuit. How much memory each cell can store depends on the type of cells an SSD uses. The most popular ones are SLC, MLC, TLC, and QLC. These stand for Single-Layer Cell, Multi-Layer Cell, Triple-Layer Cell, and Quad-Layer Cell.
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There’s a finite number of times that a cell can be read to and written from before it stops working. This is usually on the scale of several hundred thousand reads and writes, known as TBW (Total Terabytes Written). However, it does mean that SSDs have a finite limit to their usability, even if it can take several years to get there.
A first look at Backblaze’s data gives the impression that SSDs are indeed more durable than HDDs, but the average age of the mechanical drives is much higher here. Somewhere between 3-4x more than the SSDs.
Normalizing the drive-age, we see that the average failure rate (AFR) of HDDs is only a smidge better than SSDs. We’re talking about an AFR of 1.05% for the latter, and 1.38% for the former. During the accounted fourteen months, 17 SSDs and 25 HDDs bit the dust. On top of this, the drive days for the HDDs are a fair bit higher than the compared SSDs.
This proves that as SSDs get cheaper, they’re becoming less durable (though not less than HDDs just yet). With QLC NAND, PCIe Gen 3 will be the optimal interface, as these drives won’t be able to take advantage of Gen 4 and Gen 5 from what we’ve seen. Heck, even SATA isn’t a bad option for lower-end QLC drives.