The other day at work I wanted to run a quick performance test, but I didn’t want I/O to be a bottleneck. The typical solution here is to use a ramdisk, but in my case, I was dealing with very large files, so a ramdisk wouldn’t be big enough. In fact, I didn’t care about the output at all, so ideally I’d be able to write all output to /dev/null, but that wasn’t possible in this test (for example, the system will automatically append a file extension to your filename).

If I wanted to, I could have made a few code changes to get my test to work properly, but a little googling revealed nullfs, a FUSE file system which is supposed to be a big black hole, and it seemed like the perfect solution to my problem. I quickly found out it wasn’t:

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