Google has blamed a bug in a storage software update for weekend interruptions to its Gmail service in which thousands of users lost e-mail contacts and folders.
Google said initially that less than 0.08% of all Gmail users, about 160,000 people, were affected by the bug, but the latest updates have revised the proportion of affected users to 0.02% or 40,000.
"When we discovered the problem, we immediately stopped the deployment of the new software and reverted to the old version," said Ben Treynor, Google vice-president of engineering and site reliability czar.
"The good news is that e-mail 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," he wrote in a blog post.
Treynor says that even though Google keeps multiple copies of the data in multiple data centres, software bugs can affect several copies of the data.
To protect data from these types of bugs, Google also uses tape back-ups, but restoring this data takes longer than transferring requests to another data centre.
Treynor says Google will post a detailed incident report outlining what happened to the Apps Status Dashboard, as well as the corrective actions the company is taking to prevent it from occurring again.