The 2-Node Cluster Dilemma: Gateway Arbitration vs. a 3-Node Minimum for Enterprise Production?

When designing a new Sangfor HCI architecture, we often face budget constraints that push clients toward a 2-Node Cluster Deployment. Sangfor elegantly supports this by using Gateway Arbitration (filling in the Gateway IP during virtual storage initialization) to identify split-brain scenarios and determine which node remains active if a cluster heartbeat breaks.

However, looking at the structural hardware layer, a 3-Node Cluster introduces a dedicated Storage Network Interface Switch topology where voting quorum is absolute, and data rebuild limits are far more forgiving.

Let's look at the mathematical reality of Virtual Storage Available Capacity Optimization:

• For a 2-Copy Policy, the formula is: Total Data Disk Size / 2 * 85% = Available Storage.
• If a single node fails in a 2-node cluster, your redundancy is entirely gone until hardware replacement arrives, whereas a 3-node cluster can still maintain structural balancing.

  
  

  
  
  
  

My questions to the community:

• Do you ever sign off on a 2-Node cluster with Gateway Arbitration for core enterprise production databases, or do you limit it strictly to Edge/ROBO sites?
• If a network flap occurs and the 2-Node cluster triggers arbitration, have you noticed any performance degradation on the node that handles the forced VM failover?
• What is your standard policy for adjusting the optimized disk grouping (Cache SSD to Data HDD ratio) when initializing a minimal 2-node footprint?

  
  

  
  
  
  

. No,
. For core enterprise production databases, I generally recommend a 3-node cluster whenever budget allows. A 2-node cluster with Gateway Arbitration is a solid design for edge and branch deployments, but it operates with much less margin for error once a node fails.
. There isn't one perfect ratio, but for small 2-node deployments I generally prioritize cache more aggressively than I would in larger clusters.

No,
. For core enterprise production databases, I generally recommend a 3-node cluster whenever budget allows. A 2-node cluster with Gateway Arbitration is a solid design for edge and branch deployments, but it operates with much less margin for error once a node fails.
. There isn't one perfect ratio, but for small 2-node deployments I generally prioritize cache more aggressively than I would in larger clusters.

1. Regarding the use of a 2-Node cluster with Gateway Arbitration for core enterprise production databases, the 2-node cluster has inherent limitations compared to 3-node clusters, such as lower fault tolerance, lack of support for data rebuilding, and no support for multiple disk volumes. The 2-node + 1 witness node quorum mechanism introduced since HCI 6.9.0 helps prevent split-brain issues, but features like data rebuilding and data balancing are not supported in 2-node scenarios. These limitations suggest that 2-node clusters are more suitable for Edge or ROBO site deployments rather than core enterprise production databases that require higher availability and fault tolerance.

2. When a network flap triggers Gateway Arbitration in a 2-Node cluster, forcing VM failover, there is no explicit mention in the knowledge base about observed performance degradation on the active node after failover. However, it is noted that data rebuilding and data balancing functions are not supported in 2-node clusters, which implies that the system does not perform automatic data repair or balancing that could impact performance. Also, VM High Availability (HA) functions are supported in dual-node clusters, but management network and storage network offline scenarios limit HA capabilities. Therefore, while failover is supported, no direct evidence of performance degradation on the active node due to arbitration-triggered failover is documented.

3. For the optimized disk grouping policy during initialization of a minimal 2-node Sangfor HCI cluster, the system by default detects disks and assigns mechanical disks as data disks and SSDs as cache disks. The recommended practice is to use the default configuration, which typically follows the ratio requirements: each host must have at least one enterprise-grade SSD as cache disk and several enterprise-grade HDDs as data disks, with the SSD to HDD number ratio not lower than 1:6 and capacity ratio not lower than 1:20. This ensures sufficient cache capacity to accelerate read/write operations. Adjustments can be made if deploying multiple volumes, planning for additional disks for a second volume group. Enterprise-grade SSDs with power-loss protection are required for cache disks to ensure reliability.

In summary, 2-node clusters with Gateway Arbitration are generally recommended for Edge/ROBO sites rather than core enterprise production databases due to fault tolerance and feature limitations. No explicit performance degradation on the active node after arbitration-triggered failover is documented. The disk grouping policy should follow the default detection and recommended SSD-to-HDD ratios to optimize cache and data disk usage during initialization.

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