User's Manual

StorNext 3.1.3 Installation Guide 135
Appendix D
DQuality 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.