November 2

V7000: gmmaxhostdelay max_host_delay


The SVC chcluster command has a (new) option:

gmmaxhostdelay max_host_delay

Specifies the maximum time delay, in milliseconds, above which the Global Mirror link tolerance timer starts counting down. This threshold value determines the additional impact that Global Mirror operations can add to the response times of the Global Mirror source VDisks (volumes). You can use this parameter to increase the threshold from the default value of 5 milliseconds.
The Global Mirror code is designed to detect if it potentially causing performance impacts to the SVC cluster.
If it detects certain conditions, it will start to log 1920 errors and suspend relationships to prevent performance impacts.
While this may be preferable to causing host delays, dealing with 1920 errors and suspended pairs is also not desirable.
This tuneable was added in code to effectively allow you to make GM more willing to wait a little longer before starting to log the 1920 errors. You would only change it if you were getting 1920s and analysis of the TPC stats (esp internode latency) indicates having a slightly higher value (say 20ms) would allow the SVC to ride these small blips out.

By: Anthony

Copyright 2021. All rights reserved.

Posted November 2, 2011 by Timothy Conrad in category "SAN

About the Author

If I were to describe myself with one word it would be, creative. I am interested in almost everything which keeps me rather busy. Here you will find some of my technical musings. Securely email me using - PGP: 4CB8 91EB 0C0A A530 3BE9 6D76 B076 96F1 6135 0A1B