linux - crontab -- No space left on device

crontab -e
/tmp/crontab.KxTGwK: No space left on device

and

df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sda3            955486988 157545404 749405676  18% /
tmpfs                 37042680         0  37042680   0% /dev/shm
/dev/sda1               253871     89090    151674  38% /boot
/usr/tmpDSK            4128448    338068   3580668   9% /tmp

however I get this with df -i

df -i
Filesystem            Inodes   IUsed   IFree IUse% Mounted on
/dev/sda3            60669952 3809723 56860229    7% /
tmpfs                9260670       1 9260669    1% /dev/shm
/dev/sda1              65536      53   65483    1% /boot
/usr/tmpDSK           262144  262144       0  100% /tmp

So I can clean /tmp our with rm -rf /tmp/* but what is the difference between the two df's? and how is it /tmp is full yet not?