Quantum 6-00360-15 manual Reserve

Appendix D Quality of Service Guide

Configuration

Note: It is important to realize that the rtios and rtmb settings refer to the total amount of sustained bandwidth available on the disk subsystem. Any I/O, either real-time or non-real-time, will ultimately be deducted from this overall limit. The calculations of available real-time and non-real-time are discussed later.

Specifying rtmb in the FSM configuration file is only recommended if all I/Os are well formed (that is, a full stripe width). Otherwise, the conversion between MB/sec and I/Os/ sec using the well-formed I/O calculation could lead to unexpected results.

Reserve

To prevent deadlock, the QOS implementation never allows zero I/O/ sec for non-real-time I/O. Otherwise, a system could block with many critical file system resources held waiting for I/O to become available. This is especially true via flush-on-close I/O via the buffer cache. It becomes extremely difficult to diagnose system hangs because no I/O is available. For this reason, QOS always reserves some amount of I/O for non-real-time I/O.

The minimum amount of non-real-time I/O reserved for non-real-time applications is one MB/sec. This can be changed via the stripe group section parameters (again, case is not sensitive). If both are specified, the lower of the two amounts is chosen. This amount is shared by all non- real-time applications on each client.

[StripeGroup MyStripeGroup]

RtiosReserve 256

RtmbReserve 2

StorNext 3.1.3 Installation Guide 140