RAID10 - which bay is which?

I had DL4100 with RAID10 (4x6Tb) till it stopped booting. Now I am planning to connect drives to a PC, virtualize RAID0 using 2 drives and copy data to somewhere (most likely Synology NAS). Which of the 4 drives are RAID0? 1 and 2 or 1 and 3?