3.8 Block Replication

Before you begin

Before you can replicate a block-based volume, you must first make sure:

• You have installed and configured the Multi System Manager (MSM) and witness service. All replicated systems must be registered to the same MSM.
• Pools with names matching the pools used by the source volume exist on the target system.
• The destination system has enough free capacity to accommodate the replicated volume (and expected growth).
• You have created replication floating IPs on both the source and target systems.
• If you are planning on replicating to an existing application and volume on the target system, the volume must be uninitialized. In other words, the target volume must not have a filesystem, share, or any mapped initiator hosts. For simplicity, StorONE recommends allowing the replication setup to create a matching application and volume name on the target system. This requires that the application and volume do not exist on the target system.
• Although it is not required for replication to work, if you want to be able to access the replicated volume at the same IP address regardless of which system is currently hosting the primary, you should have created and paired floating IPs for the volume. You can create and pair floating IPs at any time, even after replication has been configured.

For best results, StorONE strongly recommends:

• Isolating the replication network infrastructure. If possible, the replication network should be dedicated to StorONE replication traffic, and nothing else.
• Using redundant network connections for replication.
• Ensuring that the maximum latency between replicated systems is 2ms or less when using synchronous replication.

Starting replication

As mentioned in the Before you begin section, you can allow the volume replication mechanism to automatically configure an identical volume on the target system, or you can pre-create the target application and volume. For best results, StorONE strongly recommends allowing the system to automatically configure the target volume.

For automatic configuration, make sure that the target system can accommodate all characteristics of the source volume, including:

* Drive pools with identical names for all volume pools (including any tier pools and metadata pools).
* Enough drives in each pool to accommodate the source volume N+K configuration (data blocks + parity blocks).
* Enough system capacity to replicate the source volume, as well as any near-term expected growth. You can increase the capacity of the source and target pools and volumes independently by adding drives and editing the volume capacity on each system.

If you require different volume configurations on the source and target systems (such as different pool names or N+K settings), you must pre-create the target application and volume with the required settings, but you must not initialize the volume. In the StorONE system, a volume is initialized when you either add a filesystem (for NAS and object store volumes) or map the volume to a host (for block volumes).

If you pre-create a volume on the target system, make sure that the capacity and sector size settings are identical to the source volume.

To replicate a block-based volume:

Web UI

In the admin web interface, go to Replication . Click the Start button, and fill in the fields:

Volume Selection

Application: Select the application containing the volume you want to replicate.

Volume: Select the volume that you want to replicate.

Target System: Select the target system that you want to replicate to.

Source Floating Ip: Select the replication floating IP entity that you want to use for replication. Most deployments use just one replication floating IP entity per system. In a highly available (HA) deployment, the replication floating IP entity defines two IP addresses: one per controller node. However, this uses a single named configuration entity, so there is only one entry to select in the drop-down menu.

Target Floating Ip: Select the target replication floating IP entity. As with the source floating IP, in most systems, there is only one target floating IP configuration entity to select that encompasses both floating IPs in an HA system.

Synchronous, Semisynchronous, or Asynchronous: Select the replication mode you want to use. For more information on these modes, see Replication overview.

Parameters

In the Parameters section, StorONE recommends leaving the fields empty to allow the replication setup to create a matching application and volume on the target system, with identical erasure coding, tiering, and metadata configurations. If you need to pre-create the application and volume (for example, to use different pool names or erasure coding (N+K) settings, you can do so, but StorONE recommends against it.

Target Application: If you pre-created an application and volume on the target system, select the application. If you do not see the application or volume, make sure that the source and target system are registered to the same Multi System Manager as described in the Before you begin section.

Target Volume: If you selected an existing application, the Target Volume field appears, and you can select an existing volume from that application. The volume must be uninitialized, meaning that it cannot have a filesystem, object store, or have been mapped to an initiator host.

After completing all fields, click Submit to start replication. You can view the progress by clicking the List button on the Replication page:

Configuring automatic failover

Automatic failover adds another layer of redundancy and application continuity for customers using the system.

This feature enables the ability to move the service of a volume to a different appliance automatically, if a failure occurs in the currently servicing primary appliance.

This ability is based on Replication of a volume and setting a Witness service.

Prerequisites:

• A volume configured with replication
• Witness feature enabled in the Multi-System-Management service

Please check Multi-System-Management service and Witness function documentation

Recommendations:

• The recommended latency between the system (appliance) and the Witness service is up to 1 Second (round trip). If a longer latency will be used, the witness service will still work but might cause the automatic failover to take longer.

After configuring the Witness service using the Replication 🡪 Witness 🡪 Settings dialogue, all the replicated volumes will be opened for service automatically in their target systems, once the primary source replication system fails.

Configuring NAS Replication

Setting up replication network

NAS replication enables access to NAS volumes when a failure occurs on the source system.

Prerequisites, in addition to the requirements listed above for Block Replication:

• NAS server configured in the target system

Recommended, as listed above for Block Replication

NAS replication provides the following options to comply with different use cases:

1. Standard NAS replication with manual failover
2. Standard NAS replication with automatic failover
3. NAS replication keeping source IP address
4. NAS replication keeping source IP address automatically

NAS replication with manual failover

When the NAS volume replication direction is changed using the Promote Primary option on the Replication menu, the target will become primary, and the volume will be opened to service on the existing NAS server using its existing floating IP.

Configuration includes the following steps as described above in the Block Replication:

• Setting up replication network
• Setting up volume replication
  • Automatic configuration
  • Customized configuration
  • Setting automatic failover - Optional

NAS replication creates the shares on the target system when issuing the Start-Replication command so there’s no need to create the shares.

NAS replication with automatic failover

The Multi-Systems-Manager is required to be installed and set up including the Witness set up and enabled for this feature to work. Please refer to the Multi-System-Manager setup and configuration section.

Adding the automatic failover functionality is possible by enabling the checkbox on the Replication 🡪 Witness 🡪 configuration dialog as described in the Setting automatic failover above.

NAS replication keeping source IP address

If the NAS server IP address(es) are required to be preserved even if a replication direction is changed. The NAS IP addresses can be moved to the target system when it becomes primary with the Floatingips 🡪 Pair dialog

On the Local Floating Ip section, choose from the drop-down menu the source floating ip name to be moved to target. On the Target Floating Ip, section, choose from the drop-down menu the target system that this Ip address will be moved when a failure occurs in the source system.

Once the target system is chosen, the target Interfaces per Node section will enable choosing the remote interface on each node. This is actually similar to configuring a new floating IP address where you need to choose on which interfaces will this (new) floating IP will work on.

NAS replication keeping source IP address with automatic failover

Adding the automatic failover functionality is possible by enabling the checkbox on the Replication 🡪 Witness 🡪 configuration dialog as described in the Setting automatic failover above.

The replication witness configuration includes the NAS/Object Floating IPs transition as a default. If automatic failover is required but IP is not to be moved to the target system – uncheck the box.

Replication 🡪 Witness 🡪 Settings