I am trying to make a backup of a very big postgresql(around 165 gb) for two days now. and at last I find out my mistake. never take a dump at same disk. it eats a lot of IO and kill all services which depends to dumped database.
first try I am dumping database to same disk and after around 6 hours web server started to giving timeout and lovely sitescope mails :) and I had to kill that process.
then I read a lot and started to dumping the database to another machine and it was smooth took around 4 hours to dump and no web server gave any timeout.
pg_dump -Fc dbname > db.backup
and I started restore like this
pg_restore -d dbname db.backup
before that I needed to recreate the db from psql. and this have not finished I must tell that pg_restore has -j parameter which gives more thread to read the dump file and you can give cpu number to -j which will work faster.