unRAID will do a clear of a disk that's added to the array if a) it doesn't have a valid preclear signature or b) the format of the drive isn't compatible with the array (usually XFS).   If you do use the preclear plugin or Docker, you do two things:   1) By running at least one full pass of preclear on a drive, you tend to discover if the drive has errors that may make it unsuitable for use within the array. This is useful for new drives that you want to validate - if you sh