Please note that this is for PAID subscribers i.e. if you are in Trial mode, you will only see the first 50 records of each area in Xero backed up and not completed Dataset as such.
To quickly check the status of the current backup, you should be able to see a Current Backup Progress section in the bottom part of your dashboard - Organisation Overview menu option. It should look something like this:
Hover over each of the dots to get a record count for that section of data.