> But that's a *one-way* elevator. Ideal elevators are two-way, aren't they?
Normally you use a one-way scan. A two-way scan is unfair, it will service
different parts of the disks diffrently. Specifically the edges will on
average have a longer wait than the central parts.
Imagine a request being placed just after the head passed the track. If it
is in the central region it will at most wait for the head to seek
1/2+1/2=1 disk (seek to the edge and back). On the periphery it will have
to wait at most 1+1=2.
A long seek does not take that much longer than a medium one using a
unidirectional scan lowers the max-norm of the wait.
Peter
-- Peter Svensson ! Pgp key available by finger, fingerprint: <petersv@psv.nu> ! 8A E9 20 98 C1 FF 43 E3 07 FD B9 0A 80 72 70 AF <petersv@df.lth.se> ! ------------------------------------------------------------------------ Remember, Luke, your source will be with you... always...
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.rutgers.edu Please read the FAQ at http://www.tux.org/lkml/