Draft Document for Review February 7, 2020 3:15 pm 8464ch08_Migrate.fm 8.10.2 CICS and IMS  As with DB2, IBM CICSfi and IMS use tapes to store logs and image copies of databases. CICS is only a data communication product. IMS includes the data communication and the  database function (IMS-DL/1). CICS uses the same DL/1 database function to store its data. CICS journals and IMS logs CICS tracks database changes in its journal data sets. IMS tracks database changes in its  online log data sets. After these data sets become full, CICS and IMS offload the logs to tape. CICS and IMS logs are sequential data sets. When offloading these logs to tape, you must  request a scratch volume every time. The logs contain the information necessary to recover databases and usually those logs are  offloaded, as with DB2, in two copies: one local and one remote. You can write one local copy  and then create the second for disaster recovery purposes later, or you can create the two  copies in the same job stream. With TS7700, you can create the local copy directly on TS7700 virtual volumes, and then  copy those volumes to non-TS7700 tape drives, or to a remote TS7700. Having a local copy of the logs that is written inside the TS7700 enables you faster recovery  because the data stays in the TVC for some time. When recovering a database, you can complete back out operations in less time with the  TS7700 because when reading logs from tape, IMS uses the slow read backward operation  (100 KBps) on real tape drives. With the TS7700, the same operation is much faster because  the data is read from TVC.  Lab measurements do not see much difference between read forward and read backward in a  TS7700. Both perform much better than on physical drives. The reason is not just that the  data is in the TVC, but the TS7700 code also fully buffers the records in the reverse order that  they are on the volume when in read backwards mode. Another benefit TS7700 provides to recovery operations is the availability of up to 496 virtual  drives per cluster. This configuration enables you to mount several logs concurrently and to  back out the database to be recovered faster. The IMS change accumulation utility is used to accumulate changes to a group of databases  from several IMS logs. This case implies the use of many input logs that ARE merged into an  output accumulation log. With the TS7700, you can use more tape drives for this function. Image copies Image copies are backup copies of the IMS databases. IMS can create only full image copies.  To create an image copy of a database, use a batch utility to copy one or more databases  to tape. With the TS7700, you do not have to stack multiple small image copies to fill a tape cartridge.  tHE USE OF one virtual volume per database does not waste space because the TS7700  then groups these copies into a stacked volume. Chapter 8. Migration  335