Good news, OneDrive users: A mere three months after Microsoft doubled the free storage tier from 7GB to 15GB, the company's ready to double your gratis storage space yet again—but only if you act quickly.

Playing off the social media whirlwind raging around iOS 8's need for 5GB-plus of hard drive space—forcing many iPhone users to delete apps and media in order to upgrade—Microsoft announced it will double OneDrive users' free storage capacity to a whopping 30GB if you enable the option to automatically back up your phone's photos to OneDrive by the end of September. (iCloud offers 5GB of free storage, in comparison.)

"We’ve been listening to the commentary about storage on the new iPhones released today and we wanted to get you more storage right away," OneDrive group program manager Douglas Pearce wrote on the OneDrive blog. "We think you’ll appreciate having more free storage while setting up your iPhone 6 or upgrading to iOS 8."

And Microsoft, no doubt, will appreciate you eating up your OneDrive storage with phone-uploaded photos, making it more likely you'll eventually become a paid OneDrive subscriber. It's still a stellar offer, sure, but one that's not entirely altruistic.

How to get 30GB free OneDrive storage

Don't let all the iPhone talk fool you: The offer also extends to Android, Windows Phone, and Windows users of the OneDrive app. You'll find the camera backup option in the Settings section of the OneDrive app, or by heading to Charms Bar > Settings > Change PC Settings > OneDrive > Camera roll on a Windows 8.1 device.

The extra OneDrive storage space shows up in your account quickly.

If you just want the free space and don't want to actually back up your photos to Microsoft's cloud—a perfectly reasonable precaution in these post-celebrity-photo-hack days—just back up all your photos to your PC, then delete them on your phone prior to enabling the OneDrive app's automatic photo backup option. Once you get your extra storage, simply disable the option again. (The additional 15GB showed up within minutes of my activating the feature on the OneDrive Android app.)

Remember: You need to activate automatic photo backups by the end of September to get the extra free storage space. You can download OneDrive here if this offer is convincing enough to make you hop on Microsoft's cloud storage bandwagon.