New data from Backblaze suggests that the reliability gap between hard drives and SSDs is not as large as previously thought and does not favor SSDs as much as some had believed. The previous difference between SSDs and HDDs was at least partially due to mismatching schedules.
The top-level data set from Backblaze is clearly based on SSDs, but this is due to the respective age of the SSDs compared to the HDDs in the example data set. Many products follow a so-called bathtub attachment: either devices fail almost immediately due to manufacturing defects or they last a long time before failure rates rise. As devices near the end of their lifespan, the failure rate increases. This forms both sides of the bathtub.
When Backblaze adjusts its dataset to match the relative age of SSDs and HDDs, much of the variance between them disappears:
Backblaze writes: “Suddenly the difference in the annualized failure rate (AFR) between SSDs and HDDs is no longer that great. In fact, each type of drive is within the other’s 95% confidence interval window. This window is quite large (plus or minus 0.5%) due to the relatively small number of travel days.
The general failure pattern for SSDs moves similarly to HDDs over time, although the peaks are slightly lower and the same overall time has not passed.
One thing to keep in mind: Backblaze’s dataset is based on its own backup business and doesn’t necessarily target every user market or even one of the most popular markets. A customer evaluating an SSD versus an HDD isn’t just concerned with a drive’s innate probability of failure over time. The question also arises as to how the drive can withstand shocks. Laptops come with quite a bit of punishment, and solid-state storage may be a lot better than rotating hard drives when it comes to withstanding bumps.
SSDs aren’t always the best choice for every task, especially when bulk capacity is more important than pure performance, but they will be the best option for most PC users, especially when it comes to primary drives. The performance advantage of SSDs is too big to ignore, and the data from Backblaze doesn’t suggest that SSDs are any less reliable than hard drives – just that there might not be much natural light between the two.
SSD manufacturers have faced other reliability issues recently. Lower-priced drives from several manufacturers ship with weaker specifications than originally shipped to the test community, with drives from Samsung, WD, and Crucial known to be affected.