Google has apologised for the problem that left thousands of Gmail users logging in to find that their email accounts were empty, and confirmed that it has turned to its tape backups to restore the data.

The internet giant has said sorry to the users affected and reassured people that their email has not been lost and is already being restored to their accounts.

"Imagine the sinking feeling of logging in to your Gmail account and finding it empty," blogged Google's Ben Treynor.

"That's what happened to 0.02% of Gmail users yesterday, and we're very sorry. The good news is that email was never lost and we've restored access for many of those affected.

"Though it may take longer than we originally expected, we're making good progress and things should be back to normal for everyone soon."

Taped up

Although there are multiple copies of the data on servers, Google has confirmed that bugs meant that it had to go to its tape backups to get back what was lost.

"To protect your information from these unusual bugs, we also back it up to tape. Since the tapes are offline, they're protected from such software bugs," added Treynor.

"But restoring data from them also takes longer than transferring your requests to another data center, which is why it's taken us hours to get the email back instead of milliseconds."

It's an embarrassing situation for Google which is battling to prove that webmail is reliable – although the fact that the data is backed up on tape may reassure some.

But the fact that multiple copies were affected in the cloud certainly gives pause for thought.