>> Nothing changes there. When OpenFire, Courier-MTA and Apache are restarted,
>> a few numbers change, but othrewise they remain unchanged pretty long. There
>> is no obvious activity that could trigger a disk write 20 times a minute...
>
> How many databases are in your pg cluster?
There are currently 19 of them, but only about 5 are used actively (queried at least once a day).