> > Couldn't you just write data and call sync?
>
> No. One of the reasons is that the sync does not propagate
> down. Devices with own caches have no way to get this information
> and use it to flush their caches.
>
> Additionally you don't always want all and everything flushed.
> Some pieces of data always need to be on disk, others can be written
> delayed or even out of order. Those are patterns that you can't
> implement without RAW devices.
An intelligent I/O system could still fuck up your software, ie. SCSI
disk set to "ulimited reorder" which is fine for filesystems but fatal
for some other things.
Ralf