[GrilledChips]

A scrub can both detect and repair damage. You don't need to set additional copies. If you don't want to buy 4TB of drives to store 2TB of data in a mirror, use a raidz instead.

In a raidz with at least one parity disk (and any number of data disks), corruption found on any data disk can be repaired immediately. For non-overlapping corruption a single parity disk is enough. If you have corruption of the same block on two different disks (extremely unlikely) then this can be repaired if you have two parity disks. (Etc. for three identically-corrupt data disks and three parity disks)

You can have eg. two parity disks and eight data disks (or more) and so long as no more than two disks are corrupted in the same block at the same time then a scrub will repair it completely.

The system of parity disks in ZFS' raidz is meant for reconstructing entire failed data disks, so fixing corruption is no big deal.