> >
> > of course requests and position in file will be padded to 4 or 8kB
>
> I don't think this is possible.
>
> Which reminds me:
> are block reads/writes  from/to disk devices cached in the buffer cache?

if r* device is used - no so i can use raw device for that.
but this is not very easy to change partitioning every hour ;)

raw file access would be nice.