Appendix D Quality of Service Guide

Configuration

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

Token Timeouts

The RtTokenTimeout parameter controls the amount of time the FSM waits for clients to respond to callbacks. In most normal SANs, the default two- second setting is sufficient. This value may need to be changed for a SAN that has a mixture of client machine types (Linux, NT, IRIX, etc.) that all have different TCP/IP characteristics. Also, large numbers of clients (greater than 32) may also require increasing the parameter.

For example, if the FSM should ever fail, the clients will attempt to reconnect. When the FSM comes back online, the amount of time the clients take to re-establish their TCP/IP connection to the FSM can differ wildly. To avoid unnecessary timeouts, the RtTokenTimeout parameter can be increased, meaning the FSM waits longer for callback responses.

If a client times out on a token retraction, the original requestor receives an error from the FSM that includes the IP address of the offending client. This error is logged to syslog, and alternatively to the desktop on Windows clients. This can help in diagnosing reconnect failures, and in determining if the token time value should be increased.

Client Configuration

When a client obtains a non-real-time I/O token from the FSM, the token allows the client a specific amount of non-real-time I/O. If the client is inactive for a period of time, the token is relinquished and the non-real- time I/O released back to the FSM for distribution to other clients. The timeout period is controlled by the nrtiotokenhold mount option on UNIX platforms, and the QOS Token Hold Time parameter in the mount options

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Quantum 3.5 manual Token Timeouts, Client Configuration