StorNext 3.1.3 Installation Guide 135
Appendix DDQuality 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.