>You probably have odds around 5% that the storage drive fails each cycle

What do you mean by cycle?

"My most recent drive [...] it should be fine for the next few years until it's time for the cycle to repeat."

The amount of time they stay on a single drive.

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.

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.

My understanding is that with the read error rate and capacity of modern hard drives, statistically you can't reliably rebuild a raid5/raidz1

Not an expert but I’ve heard this too. However - if this IS true, it’s definitely only true for the biggest drives, operating in huge arrays. I’ve been running a btrfs raid10 array of 4TB drives as a personal media and backup server for over a year, and it’s been going just fine. Recently one of the cheaper drives failed, and I replaced it with a higher quality NAS grade drive. Took about 2days to rebuild the array, but it’s been smooth sailing.

The bit error rates on spec sheets don't make much sense, and those analyses are wrong. You'd be unable to do a single full drive write and read without error, and with normal RAID you'd be feeding errors to your programs all the time even when no drives have failed.

If you're regularly testing your drive's ability to be heavily loaded for a few hours, you don't have much chance of failure during a rebuild.