Another important item to monitor is the VOB size. VOB size can impact in a couple of ways.
For an individual VOB, its size should be increasing at a stable pace. If there is a dramatic increase, it often indicates problems.
For the total size of all VOBs, if its size grows too close to the size of the file system, new disks/hardwares should be configured to support the increase. On the other hand, as the total size of VOBs increase, the backup time for ClearCase also increases. Make sure that the backup window is large enough, and the backup device has enough capacity.