Version Migration and Fallback is used for Business Critical and SWI-entitled systems to back down the software.
VM&F is a method used when performing a Teradata Database upgrade where a new image of the active boot environment is created, including a complete version of the operating system and Teradata Database software. This new image is called the alternate boot environment (ABE). After the ABE is created, PUT is used to install or upgrade software in the ABE, allowing the upgrade to proceed without disturbing the current system environment. When the system is rebooted, the ABE becomes the active boot environment, also known as the primary boot environment (PBE).
Teradata's standard upgrade practice is to utilize VM&F when upgrading operating system packages or performing a certified software list upgrade. Teradata CSR's and customers should jointly consider the benefits and considerations of VM&F during the upgrade planning process. VM&F is one of the significant benefits which Business Critical and SWI customers receive.
Benefits of VM&F
Using VM&F provides increased database availability during an upgrade, because upgrades are applied to the ABE while the database is fully accessible. There is no need to bring down the database prior to the node reboot at the conclusion of the upgrade. This allows much more flexibility in planning and scheduling an upgrade.
In addition, VM&F supports a simple and quick fallback to the previous software version should the upgrade not be successful for some reason, such as regression or performance problems. If an upgrade fails, or the system does not boot properly after an upgrade, the system can be redirected to boot from the pre-upgrade software image. This is known as falling back.
Considerations for Using VM&F
VM&F requires additional internal disk space to contain the ABE. Most newer MP-RAS and Linux systems have been configured to use VM&F, so the additional internal disk space is already configured.
If you are only installing packages that do not require a node reboot, using VM&F may extend the downtime.
Changes to the database copied by VM&F into the ABE before the reboot are not automatically reflected in the ABE, and may require special handling. When using the VM&F approach, it may be necessary to stop user access to the database for applications, such as automatic loading, or for database backup processing.