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Version: 2.10.1

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.