IBM OS/390 User Manual

There are two fundamental approaches to making your DL/I databases available
to IMS/ESA. One is to unload the database using DL/I utilities and reload it using
IMS/ESA utilities. The other is to 

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position

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your DL/I databases using DL/I and

IMS/ESA compatibility options in the DBD during a normal database
reorganization under DL/I.

Since database reorganization involves considerable processing for large and
complex databases, 

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positioning

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may offer some advantages. It can reduce the

time required to actually switch the production applications from VSE to MVS. It
can also allow alternate, not concurrent, access to the database by DL/I and
IMS/ESA applications. Both approaches are described below.

A database may be alternately accessed by VSE and MVS if the physical
organization meets certain restrictions and compatibility options are specified in
the appropriate DBDs. This allows IMS/ESA to access and update a DL/I
database. However, the database must be initially unloaded and reloaded using
DL/I utilities. If any reorganization is desired, this must also be performed under
DL/I. IMS/ESA utilities may be used to make IMS image copies, merge IMS log
tapes and execute IMS backout or forward recovery operations. Note that the
image copy tapes, change accumulation tapes, or logs are not portable between
DL/I and IMS/ESA.

To establish this environment, compatibility options must be used.

 1. Unload the database using the VSE DL/I utility.

 2. Identify and resolve any VSE VSAM incompatibilities as described in 5.6,

“VSAM Differences” on page 110.

 3. Specify IMSCOMP=YES in the DL/I DBDs describing the data portions of the

database. Note that changes to the VSAM logical record sizes will be
required. These are identified during the DBD generation.

 4. Regenerate the DBDs and ACBs in VSE.

 5. Reload the database using the appropriate VSE DL/I utility. The database

may now be accessed by VSE applications again.

 6. Specify DOSCOMP in the IMS/ESA DBDs describing primary or secondary

index portions of the database.

 7. Generate the IMS/ESA DBDs under MVS. The database is now accessible by

IMS/ESA whenever the VSAM user catalog defining it has been disconnected
from VSE and connected to MVS.

The database must be on a compatible VSAM supported device such as 3380,
3350 or 3375. FBA devices such as 3310 and 3370 are not supported by MVS.

When running in compatibility mode make sure the IMS/ESA and DL/I DBD
definitions are kept in synchronization. Do this by explicitly defining parameters
rather than letting them default. For example, CI size and record length for
IMS/ESA should be defined to be the same as the DL/l values.

Once migration is complete the DOSCOMP parameter may be removed when the
database is reorganized using the IMS/ESA utilities. There is no need to unload
under DL/I and reload under IMS/ESA in this case.

Chapter 8. Databases