When creating a high-availability cluster, it is always recommended to use two identical Synology NAS servers. However, it is possible to create a hybrid high-availability cluster using two similar Synology NAS servers temporarily before you acquire two identical Synology NAS servers. This article will cover the limitations of the hybrid high-availability cluster.

Requirements:

• To ensure the stability of the high-availability cluster, it is strongly recommended not to consume resources that exceed the specifications of both the active and passive servers.
• The number of drive bays and installed disks must be identical in both the active and passive servers.
• If a Synology Expansion Unit is connected to the active server, the disks and volume allocations in the passive server and its Expansion Unit must be identical to ensure normal auto failover or switchover.
• If the hosts have different numbers of LAN ports, you will not be able to configure the redundant ports, and the ports cannot be chosen as the cluster connection.

Services monitored in hybrid high-availability clusters:

If any of the following service fails on the active server, the system will fail over to the passive server (as long as the passive server is operating normally).

• File Services¹
  • Windows File Service
  • Mac File Service
  • NFS File Service
  • FTP Service
• iSCSI/Fibre Channel
• Synology Directory Server

Package limitations:

• Surveillance Station: If the service is switched to the server that has a lower maximum camera capacity, the IP cameras that exceed the limit will be stopped.
• Virtual Machine Manager: This package is not supported on hybrid high-availability clusters.

Hardware/system limitations:

• If a hybrid high-availability cluster is created using two Synology servers with different specifications, such as CPU frequency, RAM capacity, or maximum connections/shared folders supported, you may experience performance issues if the system service is switched to the server with the slower configuration. You may not be able to create or adjust any system configurations that exceed the specification of the switched server.

Synology NAS servers supporting hybrid high-availability clusters:

The following table lists the model combinations that support hybrid high-availability clusters and the minimum DSM version required by each model combination.^{2 3 4}