After HDD failure I replaced my iMac HDD and restored Time Machine backup. Now dropbox likes to resync all of my files, nearly 1 million of them!
Is it normal?
This issue has come up in the Dropbox forum as well, with the following answer from support:
Pause Dropbox, copy the content over. This will cause indexing and the client might even say uploading, but we're not duplicating files in the cloud. Your resync will happen much faster than a re-upload. Just make sure the folder structure remains identical.
If you did a restore from TM, you should already be past the "copy the content over" step and might just see the indexing/uploading step (which shouldn't upload).