My buddy's older QNAP box certainly does not work that way.

Stick a 1.5TB drive into it in place of a 750GB, and the new capacity of the RAID remains unchanged.

And on that box, they used a basterdized hack of ext3 internally, with extents from ext4, so the result was incompatible with resize2fs. That's the command needed to take over the new extra space.

We ended up ripping the drives out, plugging them into a real Linux box, formatting them there to full capacity, copying the data back onto them, and then put them back in the QNAP.

-ml