Comment 11 for bug 504632

@Miron Cuperman, I see what you are saying. However, if an application wants to ensure that at flush time the data finds its way on the hard disk rather than the disk cache then the disk caches should be turned off (as you mentioned in your description, this gives you the correct performance). Also the only other method is to have a power backed up cache.
Please refer to: http://xfs.org/index.php/XFS_FAQ for more details.

As, I mentioned before, you are seeing the speed difference in data=journalled mode probably because of more data that has to be written. This mode does not ensure that your data finds its way onto the harddisk instead of the disk cache. I believe that a filesystem would not ensure that data finds its way straight to the disk rather than the cache. This same option can be obtained by disabling the disk cache (and hence not needed to be implemented in the FS) So, if the data base application _MUST_ have the data on disk, it should simply turn off the disk cache (and get a performance hit) or have power backed up cache.

I am marking this bug as invalid, as this behavior of data going into the cache when disk cache is enabled, is expected behavior for ext[3-4]