Have you ever unplugged the wrong drive and then had to rebuild the entire array? It may not be a big deal in some ways but it does make your system vulnerable until the rebuild is done.
Many distros often enable the "bitmap" feature and this basically keeps track of what parts need to be resynced in the case of a temporary removal of a drive from the array, this way it only needs to sync what has changed.
To enable bitmap to speed up rebuilds and sync........
I separated the 2 drives in the RAID 1 array.
1 is the old one /dev/sda and is out of date, while the separated other one /dev/sdc was in another drive and mounted and used with more data (updated).
I wonder how mdadm will handle this:
usb-storage: device scan complete
md: md127 stopped.
md: bind
md: md127: raid array is not clean -- starting background reconstruction
raid1: raid set md127 active with 1 out of 2 m........