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32.1.3.5 Migrate the SNA Network Early
If the migration plan includes converting an SNA communications network, then
consider migrating ownership of the network from VSE to OS/390 within the two
months that precede operating system switchover. At this time, switchover
minus two months, the OS/390 system should be positioned for and nearly
production ready. Assuming there is connectivity between the systems, the
testing phase path has been from VSE to OS/390. After the ownership change of
the network the path is from OS/390 to VSE.
This is a good task to perform as early as possible before switchover. Switching
ownership of the network early provides some important benefits, including:
•
Reduces the size and complexity of the conversion tasks on switchover day
through dividing the conversion into smaller subtasks.
•
Eliminates having to fix network problems on switchover day.
•
The operations staff get experience on the OS/390 console.
•
If new products such as NetView are installed the staff also gets experience
with these.
•
Builds migration team confidence through the successful subtask conversion.
32.1.3.6 24x7 Installations
The major conversion challenge in a 24x7 installation is the limited window of
allowable time for testing and switchover. Typically the biggest consumer of time
during testing and switchover is the data or file migration. Therefore this is the
area to focus on to achieve time reductions during conversion. Methods to
shorten the window need to be found and exploited. In a 24x7 installation the
impact comes from having to stop the VSE production operations during the
window in which you are moving data. You can′t copy data while VSE production
is running.
One additional element that increases the duration of the data transfer, is that
backups should be run in case a fallback to VSE is necessary. If you migrate
using tapes, then these tapes can be used. The use of tapes can be quite
lengthy. One way to shorten the window where tapes are used is to orchestrate
the process right down to a drill to maximize the use of the tape drives, tapes
and people.
Additional testing and switchover timing considerations are:
•
Time must be allotted for recovery and backout in the case of problems.
•
Changes to hardware configurations and JCL can increase the duration of
conversion. Examples include RJE stations where you have to change the
JCL in them and the configurations of the PCs that are doing file transfers.
•
Screen scraper applications are also affected. End users will be accustomed
to seeing PC screens that are in ICCF format. After the switchover the
screens will be in CICS or TSO formats. These need to be reconfigured
within the window for switchover.
•
For large databases it may make more sense to copy disk to disk for backup
and then convert the new volumes in place rather than use database utilities
to move the data.
One method to expedite the data migration has been the use of extra DASD
to handle the bubble associated with copying the database for switchover.
Chapter 32. Conversion Process 485