Quantum 3.5 manual Quality of Service Guide

Appendix D

Quality of Service Guide

This appendix describes how to configure and use the StorNext File System (SNFS) Quality of Service (QOS) feature. QOS allows real-time applications to reserve some amount of bandwidth on the storage system. This is known as real-time I/O (RTIO). SNFS gates (that is, throttles) non- real-time applications so their I/O accesses do not interfere with the real- time application.

QOS is a passive implementation in that it does not actively monitor a process’ activity and then schedule the process so that it receives the bandwidth it has requested. It is up to real-time applications to gate their own I/O requests to the desired rate. SNFS QOS provides a “get out of the way” gating for non-real-time I/O requests so they do not hinder the real-time requests.

QOS is fully functional in SNFS version 2.1.2 and later. Earlier versions of SNFS do not support QOS. If a pre-QOS client connects, the file system manager (FSM) logs a message to syslog. If the pre-QOS client connects while real-time I/O is in progress, the message is logged at the critical event level.

The remainder of this document explains the client and server configuration settings for QOS; describes the use of tokens and callbacks for gating non-real-time I/O; describes setting real-time I/O on a file; and discusses the performance monitoring tools that are available for diagnosis.

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