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Backblaze thinks SSDs are more reliable than hard drives

The ones used as boot drives in its datacenters seem to be, but perhaps not over time

Cloudy backup and storage provider Backblaze has found that flash SSDs are more reliable than hard drives, at least as far as the boot drives deployed in its datacenters go, but cautions this could change in future as the SSDs age.

These findings come from Backblaze's latest report detailing reliability statistics on the drives used in its infrastructure, and in this case it is only the second such report to focus on SSDs, following one the company published in March.

One of the issues the company wanted to settle is whether SSDs really are more dependable than hard drives, but the data published in March appeared to show that the SSDs were following the same pattern of failure rate as the HDDs over time, albeit with a slightly lower annualized failure rate (AFR).

The SSDs and HDDs here are all used as boot drives, rather than the disks used to store data, and Backblaze began a switch to SSDs in Q4 2018, which means that the two sets of drives are at different points in their respective life expectancy curves. To compensate for this, the company only compared SSDs that were on average one year old with HDDs that were on average one year old, and so on.

With another year of data available, the failure rate of the SSDs took a downward turn rather than continuing to follow the same failure rate as the HDDs.

"At this point we can reasonably claim that SSDs are more reliable than HDDs, at least when used as boot drives in our environment. This supports the anecdotal stories and educated guesses made by our readers over the past year or so," said Andy Klein, Backblaze principal cloud storage evangelist.

However, he warned it is "highly certain" that the failure rate of the SSDs will eventually start to rise again, and it is possible that at some point the SSDs Backblaze uses could "hit the wall" perhaps when they start to reach their media wearout limits.

"Over the coming months we'll take a look at the SMART stats for our SSDs and see how they relate to drive failure. We also have some anecdotal information of our own that we'll try to confirm on how far past the media wearout limits you can push an SSD," Klein said.

The boot drives do more than just boot up Backblaze's storage servers, of course, as they also store log files and temporary files produced by each server, and so a boot drive will read, write, and delete files depending on the activity of the storage server itself.

As of June 30, 2022, there were 2,558 SSDs in the storage servers. This compares to the 2,200 SSDs that were covered in the March report.

Looking over the quarterly failure rates for Q1 and Q2 2022, it can be seen from the respective tables that the same number of failures was recorded (7) in each quarter, despite there being more drives included in Q2 than in Q1. This is reflected in the lower AFR for Q2 than for Q1.

Klein said that for any drive model within this cohort of SSDs, Backblaze would prefer to see it represented by at least 100 drives and account for at least 10,000 drive-days (the number of days all the drives of a specific model were operational) in a given quarter before considering the calculated AFR to be "reasonable." None of the drives meet this threshold yet.

Backblaze also examined the entire lifetime data available for all the SSD models it had active in its datacenters as at the end of Q2 2022.

It found that this lifetime AFR for all of the SSDs came out at 0.92 percent, a figure that is down from the 1.04 percent for the whole of 2021, but exactly the same as the Q2 2021 AFR of 0.92 percent. Klein warned here that Backblaze likes to see a confidence interval of 1 percent or less between the low and the high confidence interval values before the company is confident about the calculated AFR.

He noted that in these figures there are three drives with a confidence interval of 1 percent or lower, and picks out the Dell drive as the best.

"It is a server-class drive in an M.2 form factor, but it might be out of the price range for many users as it currently sells from Dell for $468.65," he commented. In contrast, the other two drives are consumer-focused and ship in the traditional SSD form factor, and both are from Seagate – the ZA250CM10003 and ZA250CM10002.

As ever, Backblaze makes available the data collected and analyzed for this report on its Hard Drive Test Data page for others to examine. Anyone can download and use this data for free, provided they cite Backblaze as the source and do not sell this data to others. ®

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