Expanding chunk sizes

I recently had to restore an Online v7 database after a disk failure. I replaced the 2 gigabyte disk with a 4 gigabyte disk. The disk was split to give two equal partitions of roughly 2 gigabytes to accomodate the 2 chunks and then the database restored. Looking at the status of the spaces I'm shown one of 1022364 pages and the other of 511692 pages. What haven't I done ? Will I run out of space when the 511692 pages are used even though there are another 511000 pages available ? Can I extend the chunk ? Thanks in advance -- Graham Bartlett