Storage study says SSDs might not be much more reliable than HDDs after all

If today I had to say that it is more prone to failure between an SSD and a HDD, I would say that an SSD is less likely to fail than mechanical hard drives because they lack moving parts. But it turns out that having turntables, actuator arms, and a motor may not be a huge disadvantage when it comes to reliability, according to one study.

Backblaze is a subscription-based cloud storage and backup company that has been in business for over a decade. As such, uniquely positioned to provide data on drive failure rates and often makes its drive failure statistics available for public consumption.

The company had been exclusively using HDDs until mid-2018, at which point they started using SSDs. And it seems to have paid off for them, as they ended up swapping all HDDs to SSDs as boot drives in new storage deployments, and also to replace failed HDDs.

“In our case, describing these drives as boot drives is a misnomer, as boot drives are also used to store log files for system access, diagnostics, and more. In other words, these boot drives read, write, and delete files, ”Backblaze explains.

This allowed Backblaze to compare the failure rates of 1,666 SSDs to 1,607 HDDs, with initial data favoring the latter; There have only been 17 SSD failures since the rapid storage medium was implemented, compared to 619 HDD failures.

At first glance, it would appear that SSDs are overwhelmingly more reliable than HDDs. However, Backblaze notes that the average age of the SSD is only 14.2 months, and the oldest has been in use for 33 months. Meanwhile, the average age of HDDs is 52.4 months, with the youngest being 27 months.

“To create a more accurate comparison, we can try to control for average age and working days in our analysis. To do this, we can take the HDD cohort back in our records to see where the average age and driving days are. similar to SSDs from Q2 2021, “says Backblaze.

Here’s what it looks like when controlling the age of the drive:

Most hard drive failures occurred after a long period of time. Turning back the clock to see drive failures after about 14 months, SSDs still fail less often, but not much; they have an annualized failure rate of 1.05% versus 1.38% for HDDs.

“Where does that leave us when choosing between buying an SSD or an HDD? Given what we know to date, using the failure rate to make a purchase decision is questionable, ”says Backblaze. “Once we controlled for age and driving days, the two types of drives were similar in failure rates and the difference was certainly not enough to justify the additional cost of buying an SSD compared to an HDD.”

This does not mean that the company will use only HDD again. Backblaze highlights several other decisive factors when deciding a purchase, such as speed and consumption.

It’s also worth noting that the data is limited in scope. While failure rates don’t favor SSDs much over HDDs, it is quite possible that SSDs will become more reliable over time. Only time will tell. Also, not all units are the same. Although still interesting, the data is too limited.

That being said, none of the SSD failures were the result of write endurance or based on SMART monitoring statistics. Backblaze says that it is only at the beginning of using SMART statistics to proactively fail an SSD, which means that you boot an SSD if you think a failure is imminent. These were all reactive failures, where the drives simply stopped working.