At 11:59 AM 2/18/98 +0100, Hartmut Reuter wrote:
>I cannot really see what advantage the load balancing across spindles and
>SCSI buses should have since all I/O is synchronous. There will never be
>more than one I/O request active at a time. The only improvement you can
>get is that from disk striping which shortens the time needed for a
>single I/O.
It's not _completely_ synchronous. Writes are almost entirely asynchronous,
as are prefetches. The file server reads data in 8 KB buffers, so if you're
using the default 64 KB chunk size, the first read is synchronous, and as
many as seven subsequent reads may be asynchronous. Then, there's a final
prefetched page that sits in the buffer cache, unused, though a subsequent
FetchData RPC may pick it up before it is flushed.
>Attach times could be much shorter, if the vnode bit maps would be stored
>on disk at detach time and than during attach could just be read in
>instead of reading all vnodes to find out which ones are used and which not.
Yup.
