question about reservation and persistent reservation
Ming Zhang
blackmagic02881 at gmail.com
Tue Jan 2 16:41:34 PST 2007
* From the T10 Reflector (t10 at t10.org), posted by:
* Ming Zhang <blackmagic02881 at gmail.com>
*
On Tue, 2007-01-02 at 11:54 -0500, Knight, Frederick wrote:
> > In the process of defining persistent reservations is was not clear in
>
> > the standards as to what the reservations were associated with. At the
>
> > same time the SCSI architecture was moving from a parallel based
> > architecture to a serial based architecture. That change required a
> > clear delineation between ports and devices that was not previously
> > necessary. The end result is that the I_T nexus became a port to port
> > definition and that made all reservations port to port.
> >
> > I would suggest the only reasonable solution is the use of persistent
> > reservations in environments that contain multi-ported SCSI devices.
>
> but if all reservations (even persistent reservation) port to port, then
> this issue is still not solved in a reasonable way, why a target should
> reject a request from _same_ initiator who holds reservation but
> different port?
>
> >> This is exactly what you want. Each host O/W must control all the
> paths
> >> from the host to the device. There may be times when the host needs
> to
> >> stop I/O on only one path. The way the host does that is via a
> PREEMPT
> >> PR function that impacts only that one path.
> >>
> >> To do that, each path must register with a unique key. When the same
> key
> >> is used, the PREEMPT will impact all paths using that key. So the
> spec
> >> allows the host to have whatever level of control it wants (such as a
> >> common key for many paths, or a unique key for each path).
thanks a lot for this and the explanation in another email. i think i
grasp the idea now.
> >>
>
> even the reservation key is to identified the _only_ nexus and can not
> be borrowed by another nexus between _same_ initiator and target right?
>
--
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