You can swap data between drives by:
Add a new storage folder with the new drive
remove the old storage folder
This will cause the host to move all of the data from the one drive to the other, gracefully handling any read errors and ignoring corrupted sectors while still salvaging everything it can that is not corrupt.
I'm not sure how well the network would hold up to a DDoS attack. It's a lot to attack 100+ hosts across 5 continents, but a lot of the hosts are pretty small, so maybe not too difficult. But also, the attack would need to be sustained for a full week, which is a lot harder. As Sia continues to grow, network-wide DDoS becomes increasingly unlikely, especially as more high powered hosts get added to the network.
Total File Contract Size refers to the size of all file contracts ever created on the Sia network. The number is also misleading anymore, because (due to off-chain optimization), large file contracts will often be represented on-chain as having 0 bytes.
