The most important disk monitoring task of a database administrator
is to make sure the disk doesn't grow full. A filled data disk may
result in subsequent corruption of database indexes, but not of the
fundamental data tables. If the WAL files are on the same disk (as
is the case for a default configuration) then a filled disk during
database initialization may result in corrupted or incomplete WAL
files. This failure condition is detected and the database server
will refuse to start up.
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 and create a symlink from the original location. But
note that pg_dump cannot save the location layout
information of such a setup; a restore would put everything back in
one place. To avoid running out of disk space, you can place the
WAL files or individual databases in other locations while creating
them. See the initdb documentation and Section 5.5 for more information.
Tip: Some file systems perform badly when they are almost full, so do
not wait until the disk is full to take action.
