Some time ago I had a problem with an ExtFS partition that was not unmounting properly, which I resolved then by repairing the partition. http://www.wilderssecurity.com/threads/extfs-not-unmounting-under-10-10-5.379912/ I mentioned then how I had some problems with disk errors when using the ExtFS partition as a VMWare Fusion boot disk, suspecting a problem with Fusion. I've finally found a fix (or a workaround) for that disk error problem, and the problem isn't Fusion, it's OS X (or how the ExtFS driver handles OS X, I'm not sure). The problem turns out to be OS X's propensity to drop all sorts of hidden files on drives, things like Spotlight search indices or filesystem event logs. A good discussion of that OS X "feature" count be found here. http://blog.hostilefork.com/trashes-fseventsd-and-spotlight-v100/ When I "blocked" the creation of these files by OS X using the methods in that article, the corruption problem went away. Hurrah! One thing then article mentions is that the ".fseventsd" directory should be empty when the partition is unmounted by OS X. Well, it was definitely not empty when I looked at the directory under Linux. I'm not sure if this is a problem with OS X or the ExtFS driver. I do know that if you block the creation of ".fseventsd" stuff as instructed in the article, my disk "corruption" problem went away when booting the partition in Fusion. I'm posting this info in case it helps anyone else.