The most important disk monitoring task of a database administrator
is to make sure the disk doesn't grow full. A filled data disk will
not result in data corruption, but it may well prevent useful activity
from occurring. If the disk holding the WAL files grows full, database
server panic and consequent shutdown may occur.
If you cannot free up additional space on the disk by deleting
other things, you can move some of the database files to other file
systems by making use of tablespaces. See Section 32.6 for more information about that.
Tip: Some file systems perform badly when they are almost full, so do
not wait until the disk is completely full to take action.