If it's a mirror setup...the data reflected on drive 1 should be the same as that reflected on drive 2. There should be no difference between the two.
From wikipedia, http://en.wikipedia.org/wiki/RAID .:
"RAID 1: In RAID 1 (mirroring without parity or striping), data are written identically to two drives, thereby producing a "mirrored set"; the read request is serviced by either of the two drives containing the requested data, whichever one involves least seek time plus rotational latency. Similarly, a write request updates the stripes of both drives. The write performance depends on the slower of the two writes (i.e. the one that involves larger seek time and rotational latency). At least two drives are required to constitute such an array. While more constituent drives may be employed, many implementations deal with a maximum of only two. The array continues to operate as long as at least one drive is functioning."