RedHat 7 is prepared for kernel-2.4 and therefore comes with a huge
/dev-tree package. Until RedHat 6.2 you could use a small root-partition
(e.g. 64M) containing the system configuration data and the /dev/-tree. I
tried to upgrade such a system and got no warning/error message, that the
root file system was to small (in respect of inodes).
During the upgrade process the inodes became exhausted after installing the
dev package and further packages failed with the installation. My system
was unusable after the update process.

It is definitely necesary not only to check the disk usage in space, but
also the inode count.