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Appendix D Quality of Service Guide
Callbacks
StorNext 3.5 Installation Guide 154
Callbacks
The cornerstones of the communications between the FSM and the client
are callbacks and tokens. A callback is an unsolicited message from the
FSM to the client requesting that the client adjust its real-time I/O
parameters. The callback contains a token that specifies the amount of
non-real-time I/O available on a stripe group.
Initially, all stripe groups in a file system are in non-real-time (ungated)
mode. When the FSM receives the initial request for real-time I/O, it first
issues callbacks to all clients informing them that the stripe group is now
in real-time mode. The token accompanying the message specifies no I/O
is available for non-real-time I/O. Clients must now obtain a non-real-
time token before they can do any non-real-time I/O.
After sending out all callbacks, the FSM sets a timer based on the
RtTokenTimeout value, which by default is set to five seconds. If all clients
respond to the callbacks within the timeout value the
RTIO request
succeeds, and a response is set to the requesting client.
Figure 60 Callback Flow for
Initial RTIO Request