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I do think that, hardware failures are inevitable, but using a RAID system, should prevent such things since all data is written on 2 or more disks at the same time. The backup might be one or more days old, think of Facebook would say: " hey 1 billion users the 10x billions of images you have uploaded in the last 24h are gone, please upload them again "

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RAID is much less effective than it used to be.

Current BER (non recoverable read error rate) is around ~1/10^14.

If you lose a drive, the probability of you encountering an error when rebuilding the RAID is rapidly approaching 1 as time goes on - BERs are not decreasing nearly as fast as drive sizes are increasing.

(This assumes you are using a RAID where you can lose 1 drive and be fine. RAIDs where you can lose 2+ drives are still fine for now.)

And this isn't taking into account catastrophic controller failure, damage due to a faulty power supply / surge, etc.

RAID only works when the RAID controller doesn't screw up, or critical metadata doesn't get wiped. If the raid controller starts being the problem your data goes with it. Problem can also happen if your hypervisors filesystem / storage drivers go screwy, get corrupted or one of a million other problems.

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