I had a problem (new to me) last week. I have a ext4 (Fedora 15) filesystem. The application that runs on the server suddenly stopped. I couldn't find the problem at first look.
df showed 50% available space. After searching for about an hour I saw a forum post where the guy used
df -i. The option looks for inodes usage. The system was out of inodes, a simple problem that I didn't realize. The partition had only 3.2M inodes.
Now, my questions are: Can I make the system have more inodes? Should/can it be set when formatting the disk? With the 3.2M inodes, how many files could I have?