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Drive manufacturers often publish the AFR. From there you can do the math to figure out what sort of redundancy you need. Rule of thumb is that the AFR should be in the 1-2% range. I haven't looked at BB's data, but I'm sure it supports this.

Note, disk failure rates and raid or similar solutions should be used when establishing an availability target, not for protecting against data loss. If data loss is a concern, the approach should be to use back ups.

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You picked a weird place to reply, because that comment is just saying what "cycle" means.

But yes, I've done the math. I'm just going with the BB numbers here, and after a few years it adds up. The way I understand "peace of mind", you can't have it with a single drive. Nice and simple.

I assume by "cycle" they are referring to mtbf/afr

I am reasonably confident that "time for the cycle to repeat" is the cycle of purchasing a new drive and moving to it.

Whether that's right or wrong, when I talked about 5% failure chance per cycle that's what I meant. And 5% is probably an underestimate.

Ahh. That % would depend on fleet size. AFR should be under 1% for most drives.

I'm estimating about five years, and the context is a single drive.

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