System Data and OmniDiskSweeper

Recently when checking my Mac’s storage usage, I noticed that the System Data category had ballooned to over 250GBs. Even with 1TB of storage, this seemed excessive and I wanted to get the the bottom of what was taking up so much space.

After some research online, I learned that I had many prior versions of Xcode simulators sitting around that were no longer available to be used. These were easily pruned, and doing so freed up a dozen or so gigabytes of space, but not nearly enough to make much of a difference in the reported amount of of disk space belonging to System Data.

Next, I took a look at local Time Machine snapshots. I didn’t really want to mess with these, but I did find that deleting some large and no longer needed files that were sitting on my drive also helped reduce the size of these snapshots. Nevertheless, I still had over 200GB devoted to System Data.

I continued by looking through my ~/Library folder and its many subdirectories, convinced that the reason for the bloat must be found there, but the numbers just weren’t adding up. Finally, I tried installing OmniDiskSweeper after seeing it recommended a few times during my online searches. I ran it and within a few minutes it had indexed all of my directories and organized them more or less by size.

At first I wasn’t sure what to do with this information, because I still didn’t know what was safe to delete. But soon I saw something that I hadn’t before—OmniDiskSweeper was showing a hidden com.apple.podcasts directory within my ~/Library folder. That directory in turn had a tmp folder with many snippets of previously-streamed podcast episodes. Over 100GB worth of snippets, in fact.

I know enough about stream buffering to know that generally speaking, the way it works is that small 15 second or so pieces of a larger stream are downloaded ahead of time. The snippets I found were undoubtably of this nature, which is why they were found in such an obscure location. What still isn’t clear to me, however, is why over a year's worth of these segments were kept on my disk well after the episodes they belonged to had been listened to, deleted from the podcasts app, and otherwise forgotten.

I deleted all 100GB of these old podcast snippets and restarted my Mac. I’m happy to report that after doing so, I'm now consistently only seeing ~90GB devoted to System Data. That still feels like more than necessary, but it’s a major improvement.