Quantum 6-00360-15 manual Callbacks, Calculating Available

Calculating Available

RTIO

Appendix D Quality of Service Guide

Callbacks

When the FSM receives a request for rtio, it takes the amount reserved into consideration. The reserve amount functions as a soft limit beyond which the FSM will not traipse. The calculation for rtio is as follows:

avail_rtio = rtio_limit - rtio_current

avail_rtio -= rtio_reserve

All internal calculations are done in terms of I/O/sec.

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.

StorNext 3.1.3 Installation Guide 145