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Standard image copies

Online Consistent Copy can also use standard image copies, in addition to Instant Snapshots, to make consistent copies.

Standard image copies may be the most efficient way to make consistent copies of a large number of objects when a relatively small percentage of the data sets involved are very large. (An Instant Snapshot that takes only 3 seconds per data set is great for a 2 GB data set, but this time is not optimal for 300 40 KB data sets.)

Related topics

Example-6-Using-standard-image-copies-and-Instant-Snapshots

Operational-considerations

Use of standard image copies can have the following advantages:

  • You are not required to have special hardware or software.
  • If you are copying a lot of small data sets, standard image copies may improve performance because Online Consistent Copy can currently do more standard copies in parallel by fully exploiting

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    subtasking than Instant Snapshots. (However, for large data sets, Instant Snapshots are faster.)

Use of standard image copies can have the following disadvantages:

  • The process creates an additional copy of all small data sets.
  • The process creates issues with volume selection for new data sets.

To make VSAM consistent copies by using standard image copies, you use the OUTSIZE option and BIGDDN option to automatically make standard copies for small data sets and Instant Snapshots for large data sets as described in the 

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The OUTSIZE option works with the BIGDDN option to determine when a data set is sufficiently large to merit a different sort of output allocation. One way to use these options is to direct very large data sets to an OUTPUT command descriptor defined with DSSNAP YES. In this way, only those data sets that pass a user-specified size threshold are copied with Instant Snapshot.

A requirement to use standard image copies in Online Consistent Copy is that the job must specify a BIGDDN value that corresponds to an OUTPUT descriptor that includes a data set name (or model) to use for the output VSAM copy.

Important

If a consistent copy that was made using a standard image copy is not on snappable hardware, you can recover to it using

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. The consistent copy is a VSAM data set, and

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can recover using a VSAM data set that is not on snappable disks by using the DATAMVR option.

You can use the consistent copy for recovery by renaming data sets or using DSN1COPY. See Usage-scenarios.

You can use the UNLOAD PLUS product to unload it. (For more information, see Example-4-Unloading-consistent-data-without-an-outage.

You can also use the COPY IMAGECOPY command in the

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product to convert the VSAM consistent copy to a standard copy, and then use the standard copy for recovery.

For example, JCL, see Example-6-Using-standard-image-copies-and-Instant-Snapshots.

 

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