- Joined
- Apr 1, 2009
- Posts
- 19,192
- Qantas
- LT Gold
- Oneworld
- Sapphire
If you have the sequence 1, 2, 3. The number 1 is written to the first drive, 2 to the second, and 3 to the third. The fourth drive would hold a checksum (1+2+3) of 6. Lose any of the first three drives, and you get its number by subtracting the two that survive from the checksum.
Whilst I'm sure that's not how it actually works, you'll get the idea....
Smarter than me