Even the fastest home Internet connection may impose a cap on the amount of data you can upload and download per month. That might be 10GB for a budget satellite connection, or hundreds of gigabytes for cable or DSL service. If you find yourself approaching your limit long before the end of the month, you can curtail your data consumption without making life too inconvenient.
I didn't expect to encounter this problem myself. My cable broadband connection — the top level of residential service my ISP offers — includes a generous monthly data limit of 400GB. My family is never stingy with our Internet access, yet we'd been able to stay comfortably under that figure.
But last month, out of idle curiosity, I checked our data usage one week into the billing month and was shocked to discover we'd already burned through half our monthly allotment. To make matters worse, I knew that later in the month we'd be downloading iOS 8 (plus dozens of updated apps) on multiple devices, along with future betas of Yosemite (at 5GB a pop), and the rest of that eight-film Harry Potter set I just bought on iTunes, which weighs in at over 40GB. Oops.
I had to figure out what had been using up all that data and then take steps to fix the problem.
Finding the main culprit
My first clue came from my ISP's daily usage summary. It showed a four-day period during which our usage had gone through the roof: 30, 46, 58, and 30 gigabytes, respectively. Seeing numbers around 40GB reminded me that I'd recently created a virtual machine in VMware Fusion to test Yosemite betas, with a disk size of 40GB. For some reason, I'd stored that virtual disk at the top level of my home folder rather than its usual location, which would have excluded it from online backups. As a result, CrashPlan dutifully backed it up to the cloud.
To make matters worse, I had synced that folder to another Mac, which was also running CrashPlan and therefore backed up the same huge files again. (CrashPlan doesn't copy the same data twice from a single computer, but this deduplication feature doesn't apply across computers.) The same thing had happened with downloads of the Yosemite beta. I used up 5GB per beta for each Mac I downloaded it on, and another 5GB to back up each beta, from each Mac.
I immediately told CrashPlan to stop backing up those files. (If you use CrashPlan, too, go to the Backup tab, click Change in the Files section, and deselect anything you want CrashPlan to ignore. You can also go to Settings > Backup > Filename Exclusions to exclude files by name or extension.) But the damage was already done. I had to dramatically reduce the family's Internet consumption for the rest of the month.
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