Let's say a hardware RAID 1 controller with disks A and B was taken offline, and a file present on both disks was altered on disk B (all within an offline state). When the RAID controller is turned back on, and the user requests the altered file, what will happen? I am assuming that most RAID 1 controllers don't detect any errors until they attempt to read from that file.
Will the RAID controller identify a difference in file size/date/signature and therefore report an error, or will it pass either of the 2 disks' contents for that file, unaware of the changes?
Would the Operating System detect any errors?
Would a software RAID 1 controller act any different?
And finally, in any RAID 1 array of N disks, which disk(s) does the OS or controller actually read from? All N? Do some RAID controllers always use disk 0, will they randomly pick a disk, or do they have access to the file-system and check the integrity (even if the disk is encrypted)?