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Replication/High Availability

Using the Inherent Features of the QNAP and Synology

Replication/High Availability

Replication is all about keeping one or more data storage in sync with a single master data storage. In this instance, the master storage is the primary data storage and replicants are the secondary data storage.

On the other hand, High Availability is the ability to switch between primary and secondary data storage devices at will. This is especially critical when the primary is unavailable for whatever reason and the secondary is promoted to be the new primary.

In terms of NAS data storage devices, Replication and High Availability are features that are common in both QNAP and Synology devices. In QNAP, the technology is implemented as Real-Time Remote Replication (RTRR) or Remote Replication. In Synology devices, this technology is implemented as Synology High Availability (SHA).

RTRR and Remote Replication in QNAP NAS

RTRR is an exclusive QNAP NAS feature that helps backup new and modified files immediately to another folder on a local NAS, external drive, or remote NAS. This feature also supports backing up data from your NAS to a remote FTP server or vice versa. The overall objective of RTRR is to improve backup efficiency while reducing backup time.

Remote Replication, also known as data mirroring, ensures that your data is always available even after the primary storage server fails. It does this by bringing the remote storage online and ensuring that you continue to work at the exact point of time when the primary device storage device failed. Implementing RTRR helps keep your system in a continuous operating condition with minimal downtime.

In order to set up remote replication on QNAP NAS devices, you need to carry out two basic steps:

Step 1: Configure settings on secondary NAS

To do this, forward the NAT router port 873 towards the LAN IP of the secondary NAS. Log into the secondary NAS as administrator and change Rsync Server settings to “enable backup from a remote server to the local host.”

In addition, check the option “Authorize remote Rsync server to back up data to NAS” then enter the login details for your Rsync service. Remember to create a shared folder that will be used as the replication destination on the secondary NAS.

Step 2: Configure settings on primary NAS

After logging into the primary NAS device, open NAS to NAS under Remote Replication and “Create a Replication Job. In the pop up window, enter the job name and secondary remote server information (Name or IP address, user name, password and port number). Next, choose the source and destination folders from a drop-down menu and the data in source folder will be replicated on the destination folder.

Tap the “Backup frequency” button and specify the replication schedule, which can be daily, weekly, monthly or repeated every few hours. The “Options” button allows you to choose desired replication options. Once done, you have the option of starting the replication instantly, after which a the status of the current job will change to “Replicating,” or “Ready” if you preferred the scheduled replication job.

High-Availability Configuration with Synology NAS

Synology High Availability (SHA) implements two hosts to create a high-availability cluster where one NAS is the active server and the other is the passive server. A high-availability cluster allows the continuous replication of data in the active to the passive server. This means that mirrored copies of any files in your system exist on both hosts, and the passive server takes over all service in case the active server malfunctions or crashes.

However, before creating a high-availability cluster, you need to ensure that both hosts are identical Synology NAS models with the same DSM and package versions. While different Synology NAS can act as active and passive servers, you will experience a few limitations.

Other requirements for a high-availability cluster include:

    • Both hosts need to have identical drive capacities to reduce data inconsistencies
    • Both servers should also have the same number of drive in similar positions
    • Make sure that the NAS devices do not contain SHR format volumes
    • Hosts should have static IP addresses and within the same subnet
    • Make sure hosts have the same number of LAN ports, including extra network interface cards
    • Switch off Wi-Fi, PPoE, IPv6, DHCP server, DHCP, and proxy servers before creating the cluster

The next thing you need to consider is the connection between both hosts. For starters, use a network cable to the hosts directly to each other to create a Heartbeat connection. This connection is vital for communication as well as data replication between the primary and secondary server.

The Heartbeat connection should be connected to the same network interface on both hosts, for instance LAN 1 on primary and secondary. Ensure that you use the fastest network interface, for example if you have 10GbE interface cards on both, use them. Finally, this connection should not pass through routers or switches.

Use the remaining network interfaces to connect the hosts to your network but make sure that the connections are in the same active network. Have different switches for each host in the high-availability cluster connecting them to the network to prevent service interruptions.

With both hosts connected properly, the next steps involve creating the high-availability cluster.

Log into the primary host as the administrator and open the High Availability Manager application. This opens up the Create high-availability cluster wizard with information on how to create the physical connection between servers.

Select network interfaces that you have chosen to use for the Heartbeat connection and high-availability cluster connection. Next, enter administrator credentials of the secondary server. Specify the name of your cluster and IP address that will enable you to access the resources of the cluster. Make sure you select an IP address that is not in use by any other services on your network.

The wizard then checks if the system meets all requirements. If you have any data, LUN, or volume on the primary server, you have the option of keeping it or erasing it. Next, confirm settings you made earlier and apply.

The wizard will then present you with a set of instruction, which you have to click yes to continue before the creation of the high-availability cluster. The time it takes to create the cluster varies depending on the environment your devices are running on. When done, the wizard will present you with a screen featuring cluster information such as CPU utilization, load average, disk activity and connection status.

The SHA system may automatically trigger failover services from the primary server to the passive server. The auto failover is initiated whenever:

    • Storage space on the primary server crashes, but storage space on the secondary is functioning
    • When errors occur on the monitored service
    • In case the primary server is rebooted, shut down or both hosts lose power


A server malfunction can be caused by human error, component failure or even system malfunction, leading to service interruption that can increase the cost of running a business. In order to achieve uninterrupted availability of your data, it is critical that you take pro-active steps to reduce administration time and costs. One way of doing this is by implement Real-Time Remote Replication on QNAP and High Availability on Synology devices.