Modifying the critical mode setting using DS CLI

Complete this task to enable the critical mode setting to prevent write operations to source volumes if data cannot be copied to the target volume of the volume pair because of a permanent error. You must have Administrator authority to perform this task.

The critical mode setting is used to determine the behavior of remote mirror and copy (PPRC) pairs or consistency groups after the source and target storage units can no longer communicate or when paths between a volume pair in the specified LSS are lost. This setting is associated with the volume pairs in the LSSs that you selected. This option is available for z/OS environments only.

When you enable the critical mode setting, the volume pair is suspended and further write operations to the source volume are not accepted if data cannot be sent to the target volume. The volume pair remains in a suspended state until you correct the problem and either issue a request to resynchronize the volume pair or delete it.

If you do not enable this setting and an error occurs to the target volume, the remote mirror and copy feature suspends the copy pair, which allows the subsequent write operations to be copied to the source volume of that volume pair. The storage unit records all tracks that have changed. When the problem is resolved, you can resynchronize the volume pair.

Perform the following step to modify the critical mode setting. The example command in this task are shown in two formats. The first format shows the type of information that the command requires. The second format provides the command with declared values for the variables.

Issue the chlcu command to modify the critical mode setting. Enter the chlcu command at the dscli command prompt with the following parameters and variables:

dscli>chlcu -dev storage_image_ID -critmode enable LCU_ID

Example

dscli>chlcu -dev IBM.1750-68FA120 -critmode enable 00-0F

Note: Use the -critmode parameter only for log devices, not for devices that the system requires. In extreme cases, the host system might have to be IPLed in order to recover a device that is write inhibited. Whenever possible, use the freezepprc command as an alternative to using the -critmode parameter.

This parameter cannot be used with Global Copy or remote copy and mirror cascading volumes.

This parameter only applies to S/390 or zSeries volumes.

The following table presents an overview of how the critical volume mode works.

Critical Mode	LCU, Critical Heavy	mkpprc critmode	Description
Normal	Disabled or Enabled	Disabled	Suspends the primary volume. Allows write operations to the primary volume.
Critical Volume	Disabled	Enabled	Suspends primary volume when the last path to the secondary volume has failed. Inhibits write operations to the primary volume.
Critical Heavy	Enabled	Enabled	Suspends the primary volume when the secondary volume cannot be updated for any reason. Inhibits write operations to the primary volume.