"And the whole point of RAID is to combat that..."
Actually the whole point of RAID is to combat a MISSING drive, not a corrupt drive. Parity works when I'm lacking one bit ... not when any of my bits might be lying.
Half of the reason of ZFS is to protect against the scenarios when a drive's internal checksum should catch a data error - but the drives returns bogus data and says 'oh its good'. RAID5 can't catch that(mathematically impossible) ... RAID6 can but most implementations don't check because its expensive(extra IO and calcs)
This is the reason most of your high end SAN vendors don't just deploy RAID5/6/10 but also checksum the data themselves under the covers. They don't trust even high end SAS/FC drives.
Actually the whole point of RAID is to combat a MISSING drive, not a corrupt drive. Parity works when I'm lacking one bit ... not when any of my bits might be lying.
Half of the reason of ZFS is to protect against the scenarios when a drive's internal checksum should catch a data error - but the drives returns bogus data and says 'oh its good'. RAID5 can't catch that(mathematically impossible) ... RAID6 can but most implementations don't check because its expensive(extra IO and calcs)
This is the reason most of your high end SAN vendors don't just deploy RAID5/6/10 but also checksum the data themselves under the covers. They don't trust even high end SAS/FC drives.