Aquí las estadísticas del disco:

Filesystem            Size  Used Avail Use% Mounted on
/dev/sda4             291G   56G  221G  21% /
tmpfs                 2.0G     0  2.0G   0% /lib/init/rw
udev                   10M   36K   10M   1% /dev
tmpfs                 2.0G     0  2.0G   0% /dev/shm
/dev/sda1             183M   36M  138M  21% /boot
/dev/sda2             471M   11M  437M   3% /tmp


Para el comando top adjunto 3 estadísticas tomadas con un lapso de diferencia de 1 minuto.
-------------------------------------
-------------------------------------
-------------------------------------
top - 09:30:21 up 4 days, 23:36,  1 user,  load average: 5.25, 4.65, 3.55
Tasks: 112 total,   2 running, 110 sleeping,   0 stopped,   0 zombie
Cpu(s): 39.2%us, 38.8%sy,  0.0%ni, 12.8%id,  8.8%wa,  0.1%hi,  0.2%si,  0.0%st
Mem:   4148704k total,  3972732k used,   175972k free,   229956k buffers
Swap:  1951888k total,       36k used,  1951852k free,  2089292k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND                                                                                         
14605 root      18   0  682m 294m 7156 S   99  7.3   3161:30 java                                                                                            
10541 root      18   0  682m 307m 7168 S   93  7.6   6043:40 java                                                                                            
25091 postgres  16   0 20832  11m  10m R   57  0.3   0:24.42 postmaster                                                                                      
15624 postgres  16   0 21116  11m  10m S   37  0.3   5:47.47 postmaster                                                                                      
15499 root      18   0  685m 134m 7168 S   22  3.3   2:02.90 java                                                                                            
15605 postgres  15   0 13660 4928  516 S    2  0.1   0:10.69 postmaster                                                                                      
 1037 root      10  -5     0    0    0 S    1  0.0   1:19.67 kjournald                                                                                       
25508 postgres  16   0 20524 4708 3844 D    1  0.1   0:00.02 postmaster                                                                                      
  334 root      15   0     0    0    0 S    0  0.0   0:01.40 kirqd                                                                                           
-------------------------------------
-------------------------------------
-------------------------------------
top - 09:31:23 up 4 days, 23:37,  1 user,  load average: 4.96, 4.72, 3.64
Tasks: 106 total,   3 running, 103 sleeping,   0 stopped,   0 zombie
Cpu(s): 61.3%us, 38.3%sy,  0.0%ni,  0.2%id,  0.0%wa,  0.0%hi,  0.2%si,  0.0%st
Mem:   4148704k total,  3996356k used,   152348k free,   230164k buffers
Swap:  1951888k total,       36k used,  1951852k free,  2115716k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND                                                                                         
10541 root      18   0  682m 307m 7168 S  100  7.6   6044:38 java                                                                                            
14605 root      18   0  682m 294m 7156 S  100  7.3   3162:31 java                                                                                            
15624 postgres  25   0 21116  11m  10m R   99  0.3   6:29.36 postmaster                                                                                      
15625 postgres  18   0 21156  11m  10m R   97  0.3   5:39.00 postmaster                                                                                      
15587 root      20   0  684m 132m 7156 S    1  3.3   1:51.06 java                                                                                            
15605 postgres  15   0 13660 4928  516 S    1  0.1   0:11.40 postmaster                                                                                      
 3193 root      21   0 2182m 335m 7108 S    0  8.3  16:30.35 java                                                                                            
15499 root      18   0  685m 134m 7168 S    0  3.3   2:09.01 java                                                                                            
26188 root      15   0  2228 1156  860 R    0  0.0   0:00.03 top                                                                                             
    1 root      15   0  1944  648  552 S    0  0.0   0:01.80 init                                                                                            
-------------------------------------
-------------------------------------
-------------------------------------
top - 09:32:22 up 4 days, 23:38,  1 user,  load average: 4.93, 4.73, 3.71
Tasks: 111 total,   2 running, 109 sleeping,   0 stopped,   0 zombie
Cpu(s): 54.7%us, 38.1%sy,  0.0%ni,  7.0%id,  0.0%wa,  0.0%hi,  0.1%si,  0.0%st
Mem:   4148704k total,  3950220k used,   198484k free,   229280k buffers
Swap:  1951888k total,       36k used,  1951852k free,  2065256k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND                                                                                         
10541 root      18   0  682m 307m 7168 S   99  7.6   6045:35 java                                                                                            
14605 root      18   0  682m 294m 7156 S   99  7.3   3163:26 java                                                                                            
15624 postgres  17   0 21116  11m  10m S   77  0.3   7:08.39 postmaster                                                                                      
15625 postgres  16   0 21156  11m  10m S   53  0.3   6:21.07 postmaster                                                                                      
15587 root      20   0  684m 132m 7156 S   19  3.3   1:59.43 java                                                                                            
15499 root      18   0  685m 136m 7168 S   11  3.4   2:17.97 java                                                                                            
15605 postgres  15   0 13660 4928  516 S    2  0.1   0:12.23 postmaster                                                                                      
27245 postgres  15   0 20524 4200 3332 S    1  0.1   0:00.04 postmaster                                                                                      
    1 root      15   0  1944  648  552 S    0  0.0   0:01.80 init                                                                                            


Finalmente les comento que utilizo un script para respaldar las bases de datos cada día pero este también ha trabajado bien.
Aquí la parte de código correspondiente a ello:

# ******************************************** #
# ******** Variables para PostgreSQL ********* #
# ******************************************** #

export POSTGRESQL_MKDIR=`date +[%d_%m_%y]`
export POSTGRESQL_LOG=`date +[%d_%m_%y]%Hhrs_%Mmin`
export POSTGRESQL_HOME='/usr/local/pgsql'
export POSTGRESQL_RESP='/home/RespaldosBD'
export ACTUAL_BASE='bdactual'

# -- PostgreSQL -- #
if [ -e $POSTGRESQL_RESP ]
then
 # -- Respaldo del día actual --
 if [ ! -e $POSTGRESQL_RESP/$ACTUAL_BASE ]
 then
  mkdir $POSTGRESQL_RESP/$ACTUAL_BASE
 fi

 # -- Respaldo historico  --
 if [ ! -e $POSTGRESQL_RESP/$POSTGRESQL_MKDIR ]
 then
  mkdir $POSTGRESQL_RESP/$POSTGRESQL_MKDIR
 fi
else
 mkdir $POSTGRESQL_RESP
fi

cd $POSTGRESQL_HOME/bin
for BASE in `./psql -c "SELECT datname FROM pg_database WHERE datname NOT IN ('postgres', 'template0', 'template1') ORDER BY datname" -d postgres -h localhost -U postgres | head -n -2 | tail -n +3 | cut -d ' ' -f 2`
do
 ./pg_dump -h localhost -U postgres $BASE > $POSTGRESQL_RESP/$POSTGRESQL_MKDIR/$BASE-$POSTGRESQL_LOG.out
 gzip $POSTGRESQL_RESP/$POSTGRESQL_MKDIR/$BASE-$POSTGRESQL_LOG.out
done

rm -f $POSTGRESQL_RESP/$ACTUAL_BASE/*
cp "$POSTGRESQL_RESP/$POSTGRESQL_MKDIR"/* $POSTGRESQL_RESP/$ACTUAL_BASE/
# -- PostgreSQL -- #


