Calculating Available

RTIO

Appendix D Quality of Service Guide

Non-Realtime I/O Configuration

not be counted against the non-real-time I/O. System designers typically allow for some amount of overage in their I/O subsystem to account for non-gated files.

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.

Non-Realtime I/O Configuration

In order to reserve bandwidth for non-realtime I/O (RVIO) operations on certain clients, you must specify the amount in the QOS central configuration file. This file is located under $CVFSROOT/config/ (for example, /usr/cvfs/config). The configuration file name consists of the file system name and the suffix _rvio.opt. For example, the central configuration file name for a file system called fs1 would be fs1_rvio.opt.

The configuration doesn't affect the normal RTIO requests; it affects only the bandwidth allocation to non-RTIO requests. Note the following characteristics of RVIO:

1RTIO has higher priority and is always satisfied first. RVIO uses whatever bandwidth is left.

2RVIO reservation is not guaranteed. Instead, it is adjusted dynamically. When there are new RVIO or RTIO requests, the bandwidth reserved for clients with previous RVIO requests is readjusted. Each RVIO client will get the RVIO bandwidth reserved proportional to its request amount.

3The RVIO bandwidth allocated for a client is the total bandwidth for non-RTIO requests on the client. The bandwidth (token) will not return like a normal non-RTIO client does if it's been idle for a hold

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Quantum 3.5 Non-Realtime I/O Configuration, Calculating Available, All internal calculations are done in terms of I/O/sec