If you're like me, then you've got got a box of hard drives in your closet.

My archive of past motion graphics projects has reached 4TB. Add a photo library of 60,000+ images, 400GB of MP3s, dozens of hours of HD footage and everything else I've accrued in 10 years as a digital artist, and I've got 12TB of data — as my mom would say — spread “from hell to breakfast”.

This is where "the cloud" comes in. I think we can all agree that finding a safer place than a cardboard box to store our digital past is a good idea. There are plenty of sites out there to help you pick which cloud backup service is best of you (Online Backup Services Review, Cloud Storage Comparison Chart). But one metric that can be easily overlooked is "data retention" — whether or not, at some point in the future, they'll delete your files from their server.

Earlier this month I asked Backblaze about their data retention policy via email. Here's their reply:

"Backblaze is intended as an active, mirror backup of the files on your drive. As such, files that are deleted from your computer, or disconnected hard drives are deleted from your backup after 30 days. We do not offer any feature to retain data indefinitely."

Here's a scenario that highlights the impact this policy can have: I dig out one of my hard drives from the closet, plug it in and two weeks later it's finished uploading the terabyte of data to Backblaze's server. Months pass, and I'm feeling at ease that my hard drive is safely in the cloud.

Then, catastrophe strikes, I loose the drive and go searching for my online backup. It turns out I haven't reconnected the drive to my machine in the past 30 days, and they've taken the liberty of deleting all my data from their servers. "How much am I paying for this service?" I ask myself.

Other cloud backup services that do NOT offer unlimited data retention are Carbonite and Mozy. Three options that do are Crash Plan, OpenDrive and SOS Online Backup.

Before you spend what could be several months backing up your data to the cloud, make sure that's where it will stay.