IBM OS/390 User Manual
•
OS/390 production is realized at an early time in the migration.
When the first kernel is completed it is cut over to OS/390 production. This
could be at a very early time in the migration thus providing early OS/390
feedback.
could be at a very early time in the migration thus providing early OS/390
feedback.
However, this may not be the advantage it appears to be. Dual OS/390 and
VSE production environments exist as VSE production (of unconverted
kernels) is required. This can be a disadvantage operationally as well as
cause problems in resource (I/O) scheduling.
VSE production environments exist as VSE production (of unconverted
kernels) is required. This can be a disadvantage operationally as well as
cause problems in resource (I/O) scheduling.
Many times, because of the dual production environment, application bridges
must be built (special procedures) to allow data and catalogs to be
alternately processed by the OS/390 and then the VSE system. Also,
maintenance and development activities must be performed on both
systems, thus potentially slowing down the overall migration.
must be built (special procedures) to allow data and catalogs to be
alternately processed by the OS/390 and then the VSE system. Also,
maintenance and development activities must be performed on both
systems, thus potentially slowing down the overall migration.
•
Dedicated and rotating conversion teams are usually involved.
The system programmer contingent of the conversion team is mainly
dedicated to the migration effort. However, application programmers very
often are involved in converting their own applications with this approach.
Rotating application programmers in and out of migration efforts can be
detrimental to development activities. It can also slow down overall
effectiveness of the migration as additional time and training takes place
each time new personnel are assigned to the conversion team.
dedicated to the migration effort. However, application programmers very
often are involved in converting their own applications with this approach.
Rotating application programmers in and out of migration efforts can be
detrimental to development activities. It can also slow down overall
effectiveness of the migration as additional time and training takes place
each time new personnel are assigned to the conversion team.
•
No definite project-end date is likely to be associated with this approach.
Many times with the kernel approach, the conversion effort
″
runs out of
steam
″
before the project is completed. This happens after the important
bread-and-butter kernels are cutover. Then, priorities often change and the
lesser visible applications stay operational under VSE for long periods of
time. This becomes expensive to a company as additional resources are
involved in maintaining two operating systems and managing two production
environments. This is why the phrase
lesser visible applications stay operational under VSE for long periods of
time. This becomes expensive to a company as additional resources are
involved in maintaining two operating systems and managing two production
environments. This is why the phrase
″
it took us 18 months or two years
″
is
many times muttered about a VSE to OS/390 migration.
2.5.2.2 Single Switchover - Mass Application Migration Approach
In the single switchover - mass application migration approach, all applications
are cutover to OS/390 production at the same time. (This time is often referred to
as the
are cutover to OS/390 production at the same time. (This time is often referred to
as the
″
switchover
″.)
As applications are converted and successfully tested
under OS/390, they are
″
shelved
″
until switchover.
4
At switchover, VSE
operations stop in entirety and OS/390 operations commence. A comprehensive
conversion aid tool (that is, product) is almost always used with this approach.
Some of the advantages to the single switchover - mass application migration
approach are:
conversion aid tool (that is, product) is almost always used with this approach.
Some of the advantages to the single switchover - mass application migration
approach are:
•
OS/390 operations are deferred until project completion.
The advantage of this is that there is no dual operations. Operators run VSE
production until the conversion is over. Also, there are no special
production until the conversion is over. Also, there are no special
″
bridges
″
that have to be built between the two systems since there is no need to
move production data back and forth between VSE and OS/390 systems.
move production data back and forth between VSE and OS/390 systems.
•
A dedicated conversion team is usually associated with this approach.
4
Maintenance updates can continue to be made to these
″
converted
″
VSE applications. The changes should be made to the VSE
source programs. Later these programs will have to be cycled back through the conversion process.
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VSE to OS/390 Migration Workbook