StorageTek 6 Control Data Set Integrity During Restore, Detecting Mismatch of Control Data Sets

Switching to a Backup Copy of the Control Data Set

If you have initialized your HSC subsystem with the additional backup copies of the control data set, you can dynamically switch operation to any one of the copies without affecting the HSC and library operation.

With an operator command, you can enable or disable specific copies of the control data set. When a copy of the CDS is disabled, the specified control data set is taken offline while any of the backup control data sets are brought online; the HSC continues to run the the library installation during the switch. When a new control data set is brought online, all work within a library complex needing the control data set halts until the switch function completes. Depending on the size of the complex, this switching time can take a few minutes. However, this is a better alternative than an HSC shutdown and subsequent restore of data sets, especially in a multi-host environment.

Operator commands are available to display the status of current control data sets or to enable/disable/autoenable any copy of the control data set. Refer to the HSC Operator’s Guide for detailed information about the commands.

Switching the Control Data Set in a Multi-Host Environment

In a multi-host environment, the HSC automatically provides communications to all hosts when a control data set switch has occurred. For this communications performance to occur, the proper hardware and software must exist in the library installation and the parameter data set must specify parameters invoking utilization of the hardware and software.

Control Data Set Integrity During Restore

To take advantage of the recovery capabilities of the HSC during the restore operations, it is necessary to ensure that you have initialized a standby control data set.

Refer to Chapter 7, ‘‘Allocating and Initializing Control Data Sets’’ in the HSC Installation Guide for detailed information about installing the HSC and initializing control data sets.

Detecting Mismatch of Control Data Sets

Control data set mismatch occurs when the HSC has determined that the primary and secondary (or shadow) control data sets are not synchronized. Normally, the HSC automatically determines which copy of the control data set is valid and switches operation to that data set.

The recovery performed by the HSC is transparent to you, except for the issuance of appropriate messages to the operator. Through the messages, the operator is made aware of the switching that has occurred.

In cases where the HSC cannot determine which control data set is valid, you must run the BACKup and RESTore utilities to recover the data sets. Refer to “When CDS Copies Are Split Among Hosts After an Error” on page 213 for some special considerations concerning control data sets.

Chapter 5. Problem Determination, Diagnostics, and Recovery 389

1st ed., 6/30/04 - 312579601