Niall’s virtual diary archives – Sunday 4th March 2018

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Sunday 4th March 2018: 4.47am. Link shared: 1441637419

Back in September 2015 (1441637419), I was lamenting how three drives had failed that year, all of which were replaced by Western Digital under warranty as it was inside three years since purchase. Back then I replaced one of the failing WD Red 3Tb drives with the then mentioned Seagate ST4000DM000 4TB drives, but due to the mirror pairing only 3Tb of it was used. As I am now down to < 100Gb free, I am swapping out the 3Tb drive in the mirror pair with the 4Tb drive to gain another 1Tb of free disc space.

There have been no additional drive failures since 2015, curiously enough. Powered on hours in order of array position are: 34,487; 25,319; 39,193; 25,514; 28,727; 21,594. All are 3Tb WD Red WD30EFRX except for the last which is the aforementioned Seagate. Average age of the WD Red's is therefore about 3.5 years, and if the mortality statistics of ~8% per quarter mentioned in my 2015 post had continued, one would have expected all my WD Red drives to have died by now.

The reason that they have not is that the Backblaze statistics showed that WD Reds actually came in two types: reliable and very unreliable. Once all the very unreliable drives had died, the remaining drives proved to be very reliable. The Q1 2017 report ( had annual mortality at just 1.15%, down from about one third. That's why all my WD Red drives are still running without any issue: they made it past their warranty period :)

The Backblaze Q4 2017 report shows that the ST4000DM000 maintains its approx 3% annual failure rate since 2015 ( and that Backblaze are now actively swapping their 3Tb drives for 12Tb models to improve density.

I like to keep spare drives to hand in case any fail and I need to swap them quickly, but I did not expect a full two years to pass between buying the pair of ST4000DM000's which I am only using now. During those two years, the cost of a 4Tb hard drive dropped by about one third, or put another way, I could today buy 12Tb hard drives so my precious max eight hard drive slots could have 4x higher density than with their 3Tb current occupants.

If it took me 2.8 years to fill 3Tb, then it will take me nearly a year to fill another 1Tb. A year from now the HAMR/MAMR drives will be available, these should enable 15Tb in each drive, though for a price premium. More importantly they might drive down the cost of the 10-12Tb drives from their current > €300 each to something more reasonable i.e. < €200 each.

It looks like there is every incentive to wait and see this time, and don't jump into buying too quickly. Back when I bought those pair of Seagates I fully expected to lose all the WD Reds in short order. Just goes to show how short term statistical trends can lie to you.

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