Comparison
Active-passivevsFailback
Active-passive
the second site sits there costing money and serving nothing, and the day you need it you find out which four things were never replicated.
Keeping a secondary location ready but idle, promoted only on failure. It is simpler than active-active because there is one writer, and its weakness is exactly that it is never exercised, so its readiness is a belief rather than an observation. Regular, scheduled failovers are the only thing that turns it from a slide into a capability.
Full entry →Failback
the original site came back and moving home turned out to be harder than the failover was, because the standby now holds the newer data.
Returning to the primary after a failover, which requires reconciling whatever the secondary accepted while the primary was away. It is the half of disaster recovery that is routinely undocumented, and it is usually the riskier half, because it is planned rather than forced and everyone is tired. Many teams deliberately do not fail back, and simply treat the secondary as the new primary until the next event.
Full entry →