6-12controller Commandscontroller pause_ioTo pause all I/O activity on the currently opened controller, use thecontroller pause_io command. While I/O activity is paused,you can make changes to devices attached to the controller withoutrebooting. For example, you can add, remove, or change SCSIchannel assignments.Before using this command, you should consider the followingpoints: The controller pause_io command allows a maximumdelay of 150 seconds (that is, 2 1/2 minutes) for all I/O activityon the currently opened controller. This delay is based on aninternal driver timeout (not on any network timeout) of threeminutes. The network timeout is client-based, and different clients arelikely to have different timeout values. Thus, pausing all I/Oactivity on the open controller can cause network timeouts,particularly if the specified delay is for more than one minute. If you find it necessary to pause the system for more than aminute, then network timeouts are usually preferable torebooting. Taking the maximum delay of 2 1/2 minutes increases thechances that a network timeout will occur. If you cannotperform the hardware reconfiguration changes in less than 21/2 minutes, then you should shut down the system. Even ifyou take the maximum delay, you can usually resume the I/Osooner. This is the reason for making the pause I/O defaulttime 2-1/2 minutes. The safest amount of time (that is, timeouts are unlikely tooccur) to delay I/O operations is no more than 30 seconds.
