The IGX00024 module is installed in conjunction with the Catalog Management Hook and comprises the second method. It is used primarily to intercept DFHSM auto recall requests that should be processed by CA Disk.
Several program products, DB2 for example, issue catalog locates and look at the returned volser to anticipate the need for a data set to be restored. The program recognizes the special volser MIGRAT as the volser DFHSM uses when it archives a data set. If this information shows that the data set is archived, the program tries to directly invoke DFHSM to restore the data set. Because CA Disk functions differently from DFHSM, the products do not recognize that a data set is archived by CA Disk and can encounter errors later. This hook, in conjunction with the Catalog Management hook, provides a means of overcoming this problem.
This hook is designed to work on your system, whether or not you have DFHSM. It is automatically installed with the Catalog Management Hook.
A catalog locate is usually issued by a routine trying to establish the existence of a data set. If the locate is successful, the data set exists; if it fails, it either does not exist or it is not cataloged. The key for the catalog management hook to go to work is when the locate is issued from a selected function (dynamic allocation, for example) and the return from catalog management is successful, but the data set is cataloged to the CA Disk pseudo-volume. (The pseudo-volume‑-the CA Disk default name is ARCIVE--is an imaginary volume to which CA Disk optionally re-catalogs a data set when it is archived and scratched, to help identify the data set as being archived.) When these conditions are met, CA Disk automatically restores the data set and then returns to the requestor of the local of the real volume to which it was restored. In this way, the locate requestor is never aware that a restore operation took place. We discuss how to catalog data sets to the pseudo-volume later in these customization instructions.
Programs that check for DFHSM's MIGRAT volser can have problems during the catalog management process of auto restore. For these programs, CA Disk does not actually auto-restore the data set. It passes back the MIGRAT volser contained in the catalog entry, instead of the ARCIVE volser. This action allows the programs to issue a request to DFHSM to restore the data set. Then, CA Disk intercepts the request with the DFHSM SVC Hook and invokes an auto-restore.
CA Disk can recognize that the DFHSM request is for a CA Disk archived data sets by doing its own catalog locate. If the ARCIVE volser is returned, CA Disk was the program that archived the data set.
In the preceding description of the catalog management hook, we said that only specific functions cause auto-restores to take place. For example, it is not good to automatically restore all data sets referenced by an IDCAMS LISTCAT job. Instead, these locates are ignored by the catalog management hook so that the output listing show a volume of ARCIVE for the data set. However, CA Disk intercepts locate requests from dynamic allocation, job initiation, and certain ISPF/TSO requests.
If you use IDCAMS to delete a data set that has been cataloged to the CA Disk pseudo-volume, the data set is uncataloged from the pseudo-volume instead of being auto-restored. The return code for the IDCAMS program is set to indicate the delete was successful. If the data set cannot be uncataloged (possibly for security reasons), CA Disk attempts to auto-restore the data set, so that IDCAMS can attempt the delete.
You see in the installation section that CA Disk does not actually replace IFG0EX0A, IGG026DU and IGX00024 modules because there are other software products that also replace these modules. To allow the user to install both products, we have decided to call our modules by different names. In the installation process, you dynamically or statically relink the appropriate IBM programs and define their entry points as the CA Disk modules. We bring up this topic now because it is important if your installation is also using IBM's program product DFHSM.
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