Q: # df -h showing disk is not full but the processes not able to write files and failing.
A: #df -i showed the inodes usage is 100% and in one of the log folders there are so many files so ran out of inodes.
Moved the files to a temp folder archived to release the inodes.
Q: # df -h showing disk is full even after deleting the big files occupying space.
A: lsof shown that there are processes still holding the deleted files and stopping kernel to reclaim the disk space.