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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, shares, 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.

Setting up volume replication

Block volume replication can be configured in the following ways:

Automatic configuration – System will create the new volume in the target system with the same characteristics of the source volume:

    1. Pool configuration:
      1. Volume Pool
      2. Metadata Pool
      3. Tier Pool (when using tiering option)

For automatic configuration both source and target systems are required to have the same pools names.

    1. Performance and redundancy:
      1. N value
      2. K value
      3. Sector size

For automatic configuration, target system is required to have the sufficient number of drives to comply with the source volume N/K values.

Choose the volume to be replicated from the Replication 🡪 Start menu

In the volume selection section – choose the Appliance from the application drop-down-menu and the volume you want to replicate

Next step, choose the required target system and the source and target floating IPs names. These will be used for the data replication and for changing the replication direction when required.

Target system list is maintained by the Multi-System-Management service, as described above in the prerequisites section, all participants in replication, must be registered to the same Multi-System-Management service.

Source and target floating IP, all participants in replication are required to have a Replication-Floating-IP configured before starting replication of a volume. Configuration of replication floating IP is described above.

Last step is to choose the replication synchronization behavior radio button (Synchrounous / Semisynchrounous / Asynchrounous) .

When submit is pressed, the system will create a new volume on the target, with the same characteristics of the source volume as described above and will start to replicate the data.

The automatic replication will not create the volume mapping for the target volume. Since this may be in a different location and may be connected to a different host(s) in that location. To add the mapping use Applications 🡪 Mappings dialog on the target system.

To follow the progress, choose Replication 🡪 list and optionally the application and volume

Customized configuration – Enables using target volume with different characteristics than the source volume.

Create the target application and volume with the desired characteristics before starting the replication. 

Do not create mapping for the target volume before starting the replication

When creating a target volume before starting the replication the capacity, sector-size and block-connectivity are required to be identical to the source volume

There’s an additional step when configuring customized replication on the source system side. After choosing the volume, target system and replication synchronization behavior,

add the required setting in the Parameters section

If the target system was registered, as required, in the Multi-Systems-Management service, all the configured applications and volumes will appear in the drop-down menus, to choose from.

In the example source and target application are the same and volume names is different. This is not a requirement; both can be configured also with different names from the source.

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:

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

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