Quantum 3.5 manual Rtio Upper Bound, Reserve

Appendix D Quality of Service Guide

Configuration

RTIO Upper Bound

The limit will be specified in terms of I/Os per second (parameter Rtios) or in terms of MB/sec (parameter Rtmb). Case is not sensitive. Note that I/Os per second are I/Os of any size to the disk subsystem. Either or both may be specified. If both are specified, the lower limit is used to throttle

I/O. If neither is specified, no real-time I/O is available on the stripe group. These parameters are applied to a stripe group definition.

[StripeGroup MyStripeGroup]

Rtios 2048

Rtmb 10

The above example specifies that the storage system can support a maximum of 2048 I/Os per second at any instant, aggregate among all the clients, or 10 MB/sec, whichever is lower.

Most real-time I/O requests will be a stripe line at a time to maximize performance. Non-real-time I/Os will be a minimum of a file system block size.

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

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