Understanding MTBF

pomkon · August 18, 2017

standard 1m hours MTBF = 41666 days.
Quoting Seagate 'Historically, the field MTBF, which includes all returns regardless of cause, is typically 50-60% of projected MTBF.'

41666*50% =20833 days =57 years (24/7 nonstop)

1 year use: 365/20833 = 1.75%
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Low 0.3m MTBF =12500days
12500/ 2 = 6250 days

1 year use: 365/6250 = 4.24%
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Improper care and uses = not quantifiable

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HDD may become unstable/slow or showing signs of failure near its inevitable death, which becomes unfit for use. That threshold is different for different task. For me, i will assume I wont use a 70% old HDD.

The 2nd hand market: you can often find used 1-2 year HDD online. Usual sold prices are are at a discount of 20-25% per year. Small HDD under 1TB are ancient models or are from recent bought cheap PCs - the years used has a large variance. Those are not really suitable for everyday use except very basic builds, in that base you would buy the cheapest anyway. Larger than 4TB have not saturated the market and fairy uncommon, the risk is considerably less. Some used HDD are sold with warranties, then you know it is less than 2-3 years old.

In a bad scenario, a uncommonly low 0.3m hours MTBF used HDD for 3 years, has 13% of its life gone, assuming you will only use it until 70%. There is lots of life left to you to burn, and in practice the capacity would be too small in the next 3 years. At that point, you should sell it.

My conclusion is that I am going to stop buying new HDD/SSD/M2, for storage and everyday purpose. I know SSD/M2 performance degrade over time, but for most users and me, I doubt it would affect most users. I am going to setup a nas in the future and hopefully as many cheap ones as possible. Other computer parts however are more resilient or maybe I am mistaken.

I did not cover AFR, but perhaps some of you have something to say about that.
http://knowledge.seagate.com/articles/en_US/FAQ/174791en?language=en_US

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