14 DAY TRIAL // Linus Torvalds doesn't usually talk about things he doesn't know, so it's probably fair to imagine that, when he says that the HFS+ file system used on Mac OS X is garbage, he's not wrong.
The discussion regarding the HFS+ file system started after the Git developers found out that there was a problem. Apparently, both the NFTS and HFS+ file systems are case insensitive, and that creates a problem. The devs had to release a new version of Git a while ago that was only fixing the problems for Windows and Mac OS X systems. Linux was not affected.
This was basically a security issue, which was best described in CVE-2014-9390, and the fix for it was made available a few weeks ago. Linus also made some comments about that problem and he did more than just detail the issue. He explained point by point why HFS+ is the worst file system in existence right now and why Apple doesn't really want to fix it.
Linus Torvalds is seldom wrong
The creator of the Linux kernel and Git says a lot of things that are not too popular with some of the users, but that doesn't mean he knows not what he's talking about. In fact, he probably has a better grasp of file systems than many other developers, given the fact that the Linux kernel is built to run on pretty much anything and that he's pulling FS patches all the time.
"Quite frankly, HFS+ is probably the worst filesystem ever. Christ what [expletive] it is. NTFS used to have similar issues with canonicalizing utf8 (ie using non-canonical representations of slashes etc). I think they at least fixed them. The OS X problems seem to be fundamental. "
"The true horrors of HFS+ are not in how it's not a great filesystem, but in how it's actively designed to be a bad filesystem by people who thought they had good ideas. The case insensitivity is just a horribly bad idea, and Apple could have pushed fixing it. They didn't. Instead, they doubled down on a bad idea, and actively extended it - very very badly - to unicode," wrote Linus on Google+.
He continued to explain some of the bad decisions taken by Apple in regards to HFS+, including issues with NFD normalization. The conclusion is that Apple probably let monkeys code for the file system.