Fallback is a Teradata Database feature that protects data in case of an AMP vproc failure. Fallback is especially useful in applications that require high availability. Fallback is enabled by default when you deploy a Teradata Database VM in the public cloud. You cannot override the Fallback setting during or after table creation.
Disabling Fallback can potentially result in data loss. Maintenance and support does not include resolution for problems that result from disabling Fallback.
Fallback is automatic and transparent, protecting your data by storing a second copy of each row of a table on a different AMP in the same cluster. If an AMP fails, the system accesses the Fallback rows to meet requests. Fallback provides AMP fault tolerance at the table level. With Fallback tables, if one AMP fails, all data is still available. You can continue using Fallback tables without losing access to data. Fallback guarantees that the two copies of a row will always be on different AMPs. If either AMP fails, the alternate row is still available on the other AMP.
See Teradata Database documentation.