Seamless SMB Failover

What is Seamless SMB Failover?

Seamless SMB Failover is a process that eliminates the need for SMB clients to remount their shares after a failover event. By managing specific networking steps during the failover, the transition can occur with minimal disruption to clients. With a sufficiently short data sync period, the failover becomes nearly imperceptible to users, ensuring continuity.

How does Seamless SMB Failover work?

The Seamless SMB Failover process involves the following steps, with steps 5–7 being specific to SMB client failover:

1. Make source un-writable: Prevent new writes to the source to prepare for failover.
2. Data synchronization: Synchronize data between the source and target to ensure consistency.
3. Make target writable: Enable write operations on the target system.
4. Update DNS records: Replace the source hostname (remove the igls- prefix) with the target hostname (add the igls- prefix) in DNS.
5. Set source IP to a non-routable address: Disrupt the TCP/IP connection for the source system.
6. Client reconnects to target: Windows clients automatically re-query DNS and establish a new connection with the target system.
7. Set source IP to a routable address: Restore the source system’s IP for potential use in future failovers.

Setting the source IP to a non-routable address effectively breaks the existing TCP/IP connection. This forces Windows SMB clients to query DNS for the updated target IP address, enabling them to reconnect without manual intervention. This approach ensures a seamless transition, minimizing downtime and user impact.

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To minimize the amount of data needing to be synced, and therefore impact to clients, we recommend running a data sync prior to beginning a seamless failover.