October 3, 2017

How to Use Synology NAS for High-Availability Clusters

Written by Jeff Gaines

How Synology NAS enables small businesses with enterprise-level technology

High-availability and data redundancy is necessary in enterprise environmnets to minimize downtime caused by system malfunction, human error, or component failure. The trouble is, the cost of such a failsafe has historically been largely unreachable by small businesses, and reserved solely for enterprise environments.

Today, high-availability is within reach for any company looking to eliminate downtime, delivering enterprise power and service in an effort to reduce the costs of downtime, as well as reduce resources spent on IT administration.

Synology High Availability (SHA) gives you the opportunity to deploy a high-availability solution so that your workforce and customers can enjoy uninterrupted services.

Synology High Availability: defined

The gist of SHA is that it combines two Synology network attached storage devices into a high-availability stack, guaranteeing uninterrupted storage and service while making the most of your system availability. This in turn lowers the risk of unanticipated interruptions and downtime.

When we say high-availability, we are talking about a server solution that is designed specifically to reduce service downtime caused by server errors. SHA uses two separate servers to form a cluster, within which one server takes on the role of the “active” server, while the other remains “passive”.

In this type of configuration, data that is stored on the active server is being continuously synced to the passive server. The result is that an exact copy of all files and applications will exist on both servers. If the active server malfunctions or experiences an error or crash of any kind, the passive server takes over.



The following is a tutorial to help you create a high-availability cluster. Please read carefully before you begin.

Hardware Requirements for SHA

1. You will need two matching Synology servers: one will be the active server, the other will be the passive server.

2. If your servers do not match, they can still act in much the same fashion, however, the setup may have certain limitations.


System Requirements for SHA

1. Both active and passive servers should be matching models and should each support SHA.

2. The identical version of DSM needs to be installed on both units.


Volume, drive position and capacity:

1. The drive capacity of both servers must be the same in order to avoid data irregularities.

2. Each of the two servers must contain the same number of drives.

3. Server drive position must be identical.

4. Neither servers can contain SHR format volumes. To ensure that no such volumes exist, go to Storage Manager > Volume.


Network Environment:

1. Assign static IP addresses to each server. IP addresses should be accessible and be assigned to the same subnet. If they aren’t, errors may arise when switching to the passive server.

To change the network settings, log in to each server separately.

Go to Control Panel > Network > Network Interface

Select the appropriate network interface and proceed to Edit.

Each server must possess the same number of LAN ports. If your servers have additional network interface cards, these can also count as additional LAN ports.

**SHA does not support: DHCP server, PPPoE, IPv6, proxy servers, DHCP, or Wi-Fi. If these are present, switch them all off prior to creating your high-availability cluster.

Note: SSH and NTP server will be enabled on the active server automatically as soon as the high-availability cluster is enabled.


Cable the servers

We’ll now go through how to connect the two servers in order to create a high-availability cluster.

  1. Using a network cable, connect the two servers. This connection is the basis of the connection between the two units, allowing them to communicate and facilitating data replication from the active server over to the passive server. This connection must:
    1. Share a network interface on both of the servers. So, if one end of the cable is connected to LAN 1 on the first server, the other end must connect to LAN 1 on the other.
    2. Access the fastest network interface available. If your servers have 10GbE network interface cards, access them.
  2. Always use a direct connection between the two units. Do not pass through any routers or switches.
  3. Connect both servers to the network using the interfaces that are left. They need to be active connections and share the same network.
  4. Your servers are now ready to be paired in order to become a high-availability cluster. Proceed to the next step.

Please note: To prevent service interruptions brought about by network failure, it is recommended that you deploy more than one switch in the network environment so that each unit in the cluster can connect to its own switch.


Combine the servers and create a high-availability cluster

When your servers are properly connected, proceed to the next set of steps in order to create the high-availability cluster.

  1. First, log into the active server using an account with admin permissions.
  2. Click on High Availability Manager.
  3. Specify the server’s IP address, your admin login or username, followed by the password of the second (passive) server. **Ensure that both servers are using static IP addresses.
  4. Click Next.


Resolve errors in the event of a failover

With certain types of errors, the system will automatically switch from the active server to the passive server. This action is called a “failover”. The system might automatically initiate a failover in any one of the situations listed below.


Error 1: Crashed storage space

Failover may happen when a storage volume on the active server has gone down but the matching space on the passive server is healthy and working as it should.

The system will not go into failover if no volume exists on the crashed server.

Once the failover process has completed, take these steps:

  1. Navigate to Disk Status and ascertain which drives are missing or corrupted on the first unit, which is now the passive server.
  • If disks are missing, proceed to install drives into the appropriate slots so that both servers mirror each other with regard to the number of drives.
  • If you are able to identify crashed drives, go ahead and replace them.
  1. Check that both of your servers have matching drive configurations and that the status of all disks shows Normal or Not Initialized.
  2. Navigate to Storage Status and click on Repair in order to fix any storage space issues.

Error 2: Service error

A service error on a monitored service may cause a failover to occur.

To illustrate, if the monitored service on the active server fails or malfunctions, the system will then failover to the passive server.

If this happens, please do the following once the failover process completes:

  1. Access the Overview page.
  2. Since what was the active server has failed, it should now be the passive server. Click Manage > Shut down passive server.
  3. Once the failed server has finished shutting down, power it up again.

Error 3: Power failure

If both units fail, if power is lost, or if the active server is rebooted or shut down, failover will occur.

For example, if the active server’s power supply fails, the system will failover to the passive server, which then becomes the active server. Once the power comes back on, power up Server A, which has now become the passive server.


Maintain the high-availability cluster

Please note that daily maintenance is necessary to maintain the integrity of your high-availability cluster.

If you have any questions about SHA or high-availability server configurations, reach out today!



Jeff Gaines

Jeff Gaines

Jeff has served as an operating executive at Interlaced since 2016. He is deeply passionate about driving impact for Interlaced, for his community, and for his loved ones. In his spare time, Jeff loves spending time with his wife and son at the world famous San Diego Zoo, enjoying tacos on the beach in Baja, cheering on the San Diego Padres, adventuring outdoors and playing music with friends. Jeff’s top 3 films of all time are Point Break (the original), Road House and Field of Dreams.