Solaris

On the impacted file system do a find for 0 byte files. If they are old and have a common naming scheme you can probably delete them freeing up an inode for each file deleted.

If you find something like this, investigate to see what is creating the files and work with the programmer or script creator to make sure they eliminate the problem.

I have usually found the number of default inodes created by the system to be sufficient and it is usually just a matter of scripts or programs cleaning up temporary files created.

Yes, backup your file system and then do newfs -i


but before doing that, try to consult thoroughly with application vendor, so you don't have to do the same thing later on