RAID1: Which disk will be mirrored?

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http://serverfault.com – How does a RAID1 system determine which disk to use as the source and which disk to use as the destination when mirroring? Assume for instance the following scenario: A RAID1 array is created with two disks A and B. A is replaced by disk C, which is added to the array. Files are beeing modified as time goes by. Now B is removed and A is reinserted. Will the RAID1 system realize that A and C are out of sync? And that C is more up-to-date than A? And if not, is there a safe way to avoid the mirroring process to start immediately when disk A is inserted? (HowTos)