Escalation due to exceeding a percentage threshold for changed pages
Both the FULL AUTO and CHANGELIMIT options have two optional integral or decimal values specified as (ncrPct, fullPct). A decimal value can be specified to the hundredth’s place (1/100 of a percent). The values represent the percentage of changed pages (based on the modification indicators in the space map pages). Valid integer values range from 0 to 100. Valid decimal values are 00.00 to 99.99. Parentheses are optional. You can specify no values, one value, or two values. If these values are not specified, BMC AMI Copy uses the values of the INCRPCT and FULLPCT installation options (which allow only integer values) as defaults. The default values for these installation options are 0 percent and 50 percent, respectively. For more information, see FULL AUTO and CHANGELIMIT in Global-COPY-options.
The setting of the ESCALATE installation option has no effect on this feature. Escalation occurs when the percentage of changed pages specified by the FULLPCT installation option or the second value (fullPct) specified with the FULLPCT or CHANGELIMIT syntax option is reached and a new incremental copy is requested. If the first value (incrPct) is supplied, the estimation of changed pages is performed earlier in the process than if only the second value (fullPct) is specified. Therefore, the estimation might be lower than the actual.
When escalation occurs due to this condition, BMC AMI Copy issues message BMC47312 and return code 0.
The percentage of changed pages used as a threshold for escalation is determined by the need to conserve media or by elapsed time considerations, such as the following:
- To save media when making copies to DASD, you might want to wait until a higher percentage of changed pages exists before escalation.
- Typically, a break-even point occurs in an elapsed time when making incremental copies. Conventional copy techniques (the BMC AMI Copy default method) use random I/O to make incremental copies, and sequential I/O to make full copies (as explained in Optimizing-the-elapsed-time-for-an-incremental-copy). This might cause an incremental copy to take as long (or longer) to make as a full copy. If the elapsed time for making an incremental copy using these conventional techniques is a concern, you can use FULLPCT or CHANGELIMIT to tell BMC AMI Copy when it should switch to making a full copy.
BMC AMI Copy checks the values specified with FULLPCT or CHANGELIMIT when all other conditions have been checked and none of them have triggered escalation. BMC AMI Copy examines the space maps to calculate changed pages and estimate the size of the image copy.
You can also optimize the elapsed time for an incremental copy by using the READTYPE option, see Optimizing-the-elapsed-time-for-an-incremental-copy.