fsync on ext4 does not work

Hi all,

Somewhy fsync does not work for me.

PgSql 9.1.2

Debian, 2.6.32 kernel

WAL filesystem: ext4 with defaults

config:
fsync=on
sync_commit=on
wal_sync_method=fsync


Even though the TPS in pgbench about 700 with 1 client.
I have tried other sync methods (fdatasync, open_sync), but all are similar.
Should I disable write cache on HDD to make it work?

Have you any idea why?

Thanks,
Otto