If using a RAID 1 and if there are any inconsistencies between both disks found, data is copied from the primary disk (most likely the one with the lower port number) to the secondary disk.
1) But what if the primary disk is damaged and therefore data differences between both disks exist only due to hardware failures in the primary disk? Will then faulty data be synced to the secondary disk? Are there checksums on modern HDDs to make sure that something like this does not happen?
2) What if I build a RAID 1 from 2 USB-Sticks? Are there any mechanisms on USB-Sticks to detect read problems, so that damaged data won't get synced by the RAID to the other USB-Stick and maybe even overwrite data that is OK? Does a RAID 1 of USB-Sticks (for an embedded system) make sense at all or will they probably fail at around the same time due to the limited write endurance?