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Yes, to completely prevent any chance of data loss from 2 drives suddenly failing at the same time you'd need 3 times duplication. Note that scanner doesn't protect against sudden failures; that's why they're called "sudden". Scanner protects against the type of failures that'll take longer to kill your drive than you/drivepool will take to rescue any data you want off it. Basically there are what I'd consider to be four types of drive failure: Sudden - bang, it's dead. This is what things like Duplication and RAID are meant to protect against. Imminent - you get some warning it's coming. Duplication and RAID also protect against this type, and Scanner tries to give you enough time for pre-emptive action. Eventual - no drive lasts forever. Scanner helps with this too by notifying you of a drive's age, duty cycle, etc, so you can budget ahead of time for new ones. Subtle - the worst but thankfully rarest kind, instead of the drive dying it starts corrupting your data. Scanner can sometimes give clues, otherwise you need some method of being able to detect/repair it (e.g. some RAID types, SnapRAID, PAR2, etc) or at least having intact backups elsewhere. DrivePool might help here, depending on whether you notice the corruption before it gets to the other duplicate(s). If it helps any, I suggest following the old 3-2-1 rule of backup best practice, which means having at least three copies (production and two backups), at least two different types (back then it was disk and tape, today might be local and cloud) and at least one of those backups being kept offsite, or some variant of that rule suitable for your situation. For example, my setup: DrivePool with 2x duplication (3x for the most important folders) to protect against sudden mechanical drive failure on the home server. Pool is network-shared; a dedicated backup PC on the LAN takes regular snapshots to protect against ransomware and for quick restores. Pool is also backed up to a cloud provider to protect against environmental failures (e.g. fire, flood, earthquake, theft).