Summary and comparison of alternative multiple port management proposals
Bob.Snively at Eng.Sun.COM
Mon Nov 21 23:54:22 PST 1994
From: Bob Snively
Date: November 22, 1994
Subject: Alternative multiple port implementations
To assist in selecting the set of functions to be provided for
multiple port operation, the following summary of the two
proposals is provided. Whichever combination of mechanisms
is selected, it is important that the implementation be robust,
simple, and sufficient. Elegance is best demonstrated by
simplicity, not complexity.
Please review this summary and the referenced documents and
provide feedback about the best solution to the management
of multiple port devices.
1) DUAL PORT IMPLEMENTATION
The present revision of SPC defines two functions required for dual port
operation. Identification of ports is simple, since the only possible
ports are "this one" and "not this one".
A) Dual Port Option
Section 5.3 defines the dual port option. It states that
the INQUIRY command shall have DualP bit to indicate that
dual ports are accepted. The dual port has separate isolated
paths and the service delivery function may be separated as
viewed from the two ports.
A SAM function to reset other ports is not yet defined.
B) PORT STATUS command
Section 7.13 defines a 6-byte command that performs the following
functions. The architecture assumes that there are only
two ports on the target.
a) Disables opposite port
b) Enables opposite port
c) Form logical unit reservation to port issuing command,
releasing any reservations on the opposite port.
d) Determine status of any reservations that may
exist on the target device, including the SCSI device
identifier of the initiator holding the reservation
and identification of the port to which the
reserving initiator is attached.
2) MULTIPLE PORT IMPLEMENTATION
The present revision of document X3T10/94-233 defines two functions
required for multiple port operation. The number of ports is not
limited. The mechanism for defining the ports is outside the scope
of the standards, but the following methods may be used.
Targets can be identified by their serial number or, if
supported by the SCSI protocol, their world-wide name.
Initiators communicate by methods outside the protocol to
Initiators can be identifed by their world-wide name.
For SIP devices which have only two ports, targets identify
initiators as being those installed on this port or those
installed on the other port.
All initiators bear the same relationship to a target, whether
they are one of several initiators on the same port or
on another port.
A) ABORT TASK SET, OTHER INITIATOR
This is a task management function that resets all tasks
from the specified initiator. This allows a host that
is taking over from a failing host to clear all those target
resources that had been under control of the failing host.
This function is proposed to be added to SAM, section 7.
The method for identifying the initiator is protocol dependent
and outside the scope of SAM.
B) Priority Reserve
This bit is added to the RESERVE(6) and RESERVE(10) commands
to force the release of any conflicting reservations and the
formation of the specified type of reservation to the issuing
Table of features for two approaches to multiple port management
Capability DUAL PORT MULTIPLE PORT
Number of ports 2 any number
Resource recovery tbd ATSOI
Priority Reserve logical unit any type
Initiator ID SIP compatible depends on protocol
More information about the T10