Changes to SDA Model for multiple controllers
gfredin at smtplink.wichitaks.ncr.com
Fri May 13 11:27:43 PDT 1994
The following is a list of operations needed to manage multiple
controllers in an SDA, and how they could be accomplished within the
current model. If it is not possible (or at least not apparent how) to
perform an operation, I have suggested an addition or modification to
I have assumed that there is a C-LUI type of Controller.
1. The initiator must be able to determine that there is more than one
path to an SDA. This can be accomplished by first scanning with Inquiry
commands and locating all SDA device types. For all SDA device types,
the Unit Serial Number Vital Product Data Page should be requested. If
identical serial numbers are returned, these identify paths to the same
2. The initiator needs to know for each path, which controller C-LUI is
being accessed. By using the Report C-LUI Service, the initiator can
determine what controllers the SDA contains, but there is no mechanism
to determine which controller is being accessed. A "report current
connection" or similar service to identify the addressed C-LUI is
3. If the SDA is able to take advantage of the redundant controllers
without any host intervention, then the capability is needed to specify
and/or report this sparing capability. This is available through the
Create/Modify or Report P-LUI/C-LUI Spare Service.
4. The model needs to account for implementations that:
a. Only allow access through one controller to all volumes.
The other controller is a hot standby.
b. Each volume has a dedicated access path through one of the
controllers. If one controller fails, the other controllers
can be instructed to provide an access path to the volumes
which are no longer accessible.
c. Allow access to any volume through any controller concurrently.
By providing the ability to attach volumes to the controller C-LUIs, any
of these implementations can be accomplished. The model currently
allows attachment of C-LUIs, P-LUIs, and R-LUIs to C-LUIs, but does not
address the need to attach a V-LUI to a C-LUI.
5. A service is needed which would enable and disable the controllers.
This is similar to the enable/disable port in the dual port model. If
the model allows for operations to other types of C-LUIs (turning LEDs
on/off, resetting power supply fault indicator, etc.) then the same
mechanism could be used for controller C-LUIs to provide this service.
More information about the T10