A thought about the lifetimes of hard disks and solid state disks

October 3, 2020

At work, a related group to ours just had a SSD start reaching its official total writes lifetime, and this sparked a thought (especially when combined with my goal of moving away from hard drives on my own machine).

On the one hand, it's increasingly conventional wisdom that modern solid state drives (both SSD and NVMe) have a longer expected lifetime on average than hard drives. On the other hand, you can get lucky and have individual hard drives that just keep on going and going and going, or at least this was the historical thing. Since solid state drives have a pretty strong lifetime limit for the total amount of writes that you can do to them, you'll never get lucky this way with an actively used SSD in the way that you could with a HD. All of your SSDs will definitely die sooner or later; the only question is when. You will never have a 'lucky 20 year old well used but still running' SSD.

The spoiler in this thought is that modern hard drives may not be able to reach this sort of lucky long durability for various reasons. An obvious one would be if they contain their own flash memory that's written to often enough to wear out after a certain write volume. Another would be if they're now built with materials and technology that has the same definite and irreversible decay over time that flash memory does (where you just can't get lucky).

Hardware with a definite lifetime has potential impacts on efforts to preserve systems and keep them operating for historical purposes over the long term. People have done impressive things to get very old systems from the 1960s, 1970s, and so on running so that we can actually see these influential and historical systems for ourselves. Probably that will be as possible in the future, though, since most of those historical systems that people are bringing back haven't been running continuously since then.

Some grumpy sysadmins will also consider it a feature that if you put a system in a closet and leave it there for five or ten years, it will probably die instead of hanging around as an ancient zombie full of outdated things. The downside of this is for 'industrial' computers that are embedded into larger systems (including in things like hospital machinery, which are infamous for still running their embedded computers with long-obsolete operating systems). Perhaps the hardware vendors will just vastly over-provision the SSDs and then hope for the best.

Comments on this page:

By WonderThingBlue at 2020-10-03 08:20:03:

But is the SMART value you monitor the amount of data written to the drive or an actual wear-levelling indicator? One would be whatever the manufacturer guarantees the drive is capable of, the other is a better (but not always good) estimate of the actual remaining lifetime.

In a long-term test in a german computer magazine of SSDs of various brands in 2017, even the worst one managed 2.5 times its specced TBW and the best one only started reporting read/write errors after more than 8000TBW even though it was only specified for 150.

By Randall at 2020-10-04 02:00:42:

You can still get SLC drives mostly for long-life use like you mention. Lot pricier per GB, but a lot cheaper per write cycle if that's what you're looking at.

Written on 03 October 2020.
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