Failed Time Machine Backups Fill Up Your Internal Drive Too

A failed Time Machine backup stops macOS from releasing an old local snapshot, and that snapshot retains everything you delete. A snapshot doesn’t store data. It just prevents blocks from being freed. Every file that is deleted since that snapshot was taken has its blocks pinned by it. In my case, my backups had been failing since March (it’s July) so the old snapshot was never released. This old snapshot ballooned up to 226GiB. I thought anything related to failed Time Machine backups would only take up space on the external SSD that I use for backups, but that is not the case. While macOS did warn me that my backups were failing due to my external drive being full, it never said anything about the same failure taking up 226GiB on my local drive. The other misleading part is that deleting files wasn’t actually freeing up space! Before I cleared the old snapshot, this is what my storage looked like. There were 974GiB used. At this time, I didn’t know that 226GiB were being taken up by…