i fail to see the point in using hadoop if your universe is limited to foreign exchange... you can probably fit all ticks of all pairs in existence since the 70s in less than a TB
I've assumed only outright ticks, hence the 40 pairs - in reality most banks store the crosses as well, which can be up to 1,600 pairs (40 x 40), which will get you into the PB range for the 40 years.
(1 + 4 * 10) * 8 = 328 bytes
Note that the "tick data" from histdata.com gives you prices sampled every 1 second (so not every tick) for the top level of the order book, and doesn't give you any size information at all.