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Appendix D Quality of Service Guide
Callbacks
StorNext 3.1.3 Installation Guide 146
Figure 60 Callback Flow for
Initial RTIO Request
In the above diagram, a process on client A requests some amount of
RTIO in Step 1. Since this is the first request, the FSM issues callbacks to all
connected clients (Steps 2-5) informing them that the stripe group is now
in real-time mode. The clients respond to the FSM in Steps 6-9. After all
the clients have responded, the FSM responds to the original requesting
client in Step 10.
If the timer expires and one or more clients have not responded, the FSM
must retract the callbacks. It issues a response to the requesting client
with the IP number of the first client that did not respond to the callback.
This allows the requesting client to log the error with the IP number so
system administrators have a chance of diagnosing the failure. It then
sends out callbacks to all the clients to which it first sent the callbacks,
retracting them to the original state. In our example, it would set the
stripe group back to non-real-time mode.
After sending out the callbacks, the FSM waits for a response using the
RtTokenTimeout value as before. If a client again does not respond within
the timeout value, the callbacks are retracted and sent out again. This
repeats until all clients respond. During this time of token retractions,
real-time requests cannot be honored and will only be enqueued.