Optimizing the elapsed time for an incremental copy

Although making an incremental copy conserves media, it might take longer than a full copy, even at low percent change rates (5 to 20%). This is largely due to the conventional random I/O read method used for incremental copies, compared with the sequential I/O read used for full copies.

When you use the READTYPE option, you can either choose which type of reading (RANDOM or FULLSCAN) BMC AMI Copy will use, or you can specify AUTO to let BMC AMI Copy automatically make the choice for you:

• Using READTYPE RANDOM (the BMC AMI Copy default) tells BMC AMI Copy to use the conventional method for incremental copies.

• Specifying READTYPE FULLSCAN tells BMC AMI Copy to perform a full table space scan to determine which pages have changed. If you know a space has changed sufficiently to make random I/O inefficient, you should use FULLSCAN.

  Important

  The FULLSCAN option is valid only with RESETMOD NO. If a table space is defined with TRACKMOD NO, READTYPE FULLSCAN and RESETMOD NO are automatically set.

• Specifying READTYPE AUTO enables BMC AMI Copy to make the choice according to the number of changed pages (based on the modification indicators in the space maps). For spaces with sporadic update activity, this provides the best reading technique for the current condition of the table space.

  When you specify READTYPE AUTO, you can also use READPCT to tell BMC AMI Copy the percentage of changed pages at which to escalate from random I/O to a sequential table space scan. The default for READPCT is the value of the installation option of the same name, which defaults to 10%.

  Important

  You should only use READTYPE AUTO when your full copy strategy uses RESETMOD YES.

  For more information about READTYPE and READPCT, see Global-COPY-options.  Also, Full image copy versus incremental image copy shows how elapsed time varies with the technique employed to make incremental copies.