I know that this is going to be time consuming and prone to human error, so I use a paid service (MultSync) to sync the drives.
I choose the option to move files from Dropbox to Google Drive.
The files seem to copy over ok, but nothing is moved off the Dropbox drive.
This means that I can't tell whether everything has been copied off Dropbox or not.
Multsync is also giving me errors about some files not being able to be copied due to legal issues.
I realise that Multsync is in China and feel stupid for having exposed all my data to the Chinese Government.
This is a bad move. I should have waited to evaluate the performance of the new storage platform first. But I was impatient.
A list of changes would have been useful at least.
As a result I now need to try and apply the new directory structure to Dropbox, but it's not obvious what is different.
I install Cloudless on my Android, but while I seem to get accurate folder sizes for Dropbox, the output for Google Drive is nonsensical, with no obvious hierarchy. So I cannot compare Dropbox and Drive folder by folder.
I have to leave the files on Google Drive until the Dropbox sync has finished, in case Dropbox deletes files which it thinks I already threw away.
I try both the Google Drive client and the Insync client. Both are horribly slow and sit there counting files.
I move the folders back into the Dropbox directory.
Dropbox syncs speedily, with 4 concurrent transfers.
However Dropbox has synched the removed folders and does not recognise them (or their children?) anymore.
So these are now added to Dropbox with the affix '(Selective Sync Conflict)'.
A lot of folders are affected by this.
I buy 'Araxis Find Duplicate Files' from the App Store, to identify any files which have been created in the last few weeks.
Downloading files that are only Google Drive now is difficult too. I get an error when trying to download files via the web interface, apparently I am supposed to use the Drive app. But the Drive app doesn't offer the fine-grained control over sync Dropbox does. It's all or nothing, and the Insync counter moves so slowly, so it's nothing.
Dropbox shows a sea of green but some folders are not synched with Dropbox.com.
After pausing and unpausing the synch, and a bunch of folders now show the synching icon instead.
Grrr.
Araxis Find Duplicate Files
Find EmptyFolders 1.1 (free)
Araxis Merge (free 30 day trial)
Copy from Folder B to Folder A