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Comment by louwrentius | Hacker News Reader

It can be luck, but with 24 drives, it feels very lucky. Somebody with proper statistics knowledge can probably calculate the risk with a guestimated 1% yearly failure rate how likely it would be to have all 24 drives remaining.

And remember, my previous NAS with 20 drives also didn't have any failures. So N=44, how lucky must I be?

It's for residential usage, and if I need some data, I often just copy it over 10Gbit to a system that uses much less power and this NAS is then turned off again.

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We don't really have to guess. Backblaze posted their stats for 4 TB HGST drives for 2024, and of their 10,000 drives, 5 failed. If OP's 2014 4 TB HGST drives are anything like this, then this is just snake oil and magic rituals and it doesn't really matter what you do.

> If OP's 2014 4 TB HGST drives are anything like this, then this is just snake oil and magic rituals and it doesn't really matter what you do.

It might matter what you do, but we only have public data for people in datacenters. Not a whole lot of people with 10,000 drives are going to have them mostly turned off, and none of them shared their data.

5 drives failed in Q1 2024. 8 died in Q2. That is still a very low failure rate.

Drives have a bathtub curve, but if you want you can be conservative and estimate first year failure rates throughout. So that's p=5/10000 for drive failure. So chance of no-failure per year (because of our assumption) is 1-p. So, chance of no-failure per ten year is (1-p)^10 or about 99.5%

Is that for one drive, or for all 24 drives to survive 10 years?

That's for one drive. For all 24 it's about 88.7%.

Those are different drives though, they're MegaScale DC 4000 while OP is using 4 TB Deskstars. Not sure if they're basically the same (probably). I've also had a bunch of these 4TB Megascale drives and absolutely no problems whatsoever in about 10 years as well. Run very cool as well (I think they're 5400 rpm not 7200 rpm).

The main issue with drives like these is that 4 TB is just so little storage compared to 16-20 TB class drives, it kinda gets hard to justify the backplane slot.

it's (1-p)^24^10, where p is drive failure rate per year (assuming it doesn't go up over time). so at 1% that's about 9% or a 1/10 chance of this result. Not exactly great, but not impossible.

the backblaze rates are all over the place, but it does appear they have drives that this rate or lower: https://www.backblaze.com/blog/backblaze-drive-stats-for-q2-...

I can see that, my assumption that my result (no drive failure over 10 year) was rare is wrong. So I've updated my blog about that.

The failure rate is not truly random with a nice normal distribution of failures over time. There are sometimes higher rates in specific batches or they can start failing altogether etc.

Backblaze reports always are interesting insights into how consumers drives behave under constant load.

I'm curious what the "Stop/Stop cycle count" is on these drives and roughly how many times per week/day you are accessing the server.

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