Why is my startup disk so full? I've been getting messages recently that "My startup disk is almost full," and I'm quite sure I haven't used the full 250GB of my Macbook's hard drive. Using "Get Info" on Macintosh HD says that I'm using around 245GB (aka 5GB from being full), but I have no idea what could be using that much space. My home directory (with Photos, Movies, Downloads, etc.) is only around 34GB. Applications? only 11.

In fact, I looked into it using a disk sweeping application, and it profiled my hard drive as only having 65.1GB in total! Where are the other ~200GB? What's filling them?

(I did search using Finder for files over 1GB, and there were only a few, so I don't think the problem is one massive file).

Result of ImageDiskSweeper:
It turns out that another user account (not the one I was logged into) had many gigabytes of photos stored on the hard drive. DiskImageSweeper, along with any other tools (spotlight search, etc.) could not search through the other user's files, so they were virtually undetectable.

I solved the problem by logging into the other user account and clearing up space. I imagine that you could also just delete the user's account and have the same effect.