Request-SPOUpgradeEvaluationSite is a PowerShell command available in SharePoint online 2013 environment.

Requirement
If you want to take a copy of the entire site collection before running upgrade process, you can run the UpgradeEvaluationSite PowerShell command. You should be SharePoint online admin to run the command.

Solution:
Request-SPOUpgradeEvaluationSite http://mySites/sites/HRSites

It sends out an email message and automatically trying to upgrade the evaluation site

Request-SPOUpgradeEvaluationSite http://mySites/sites/HRSites -NoEmail $true - NoUpgrade $true

It doesn't send out any email though. But SharePoint Online global admin can make changes to the upgrade evaluation site before starting the actual upgrade.