• Replication workflow

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    Replication workflow

    Configure replication

    Replication can occur locally or between a local storage system and a remote storage system. Use the native Replication feature in Unisphere to configure replication for block or file storage resources. The system supports asynchronous and synchronous replication of all storage resources, including file systems, NAS servers, LUNs, LUN groups, VMware VMFS datastores, VMware NFS datastores, and thin clones.

    You can also configure synchronous and asynchronous replication for LUNs and VMware VMFS datastores using the RecoverPoint appliance-based solution.

    Configure local replication

    Local replication is applicable to asynchronous replication only. Local replication is not applicable to synchronous replication.

    Replication interfaces and connections do not apply to local replication. When using the CLI or the REST API, once you create the identical source and destination storage resources or NAS servers on the storage system, you can proceed to configure a replication session. When using Unisphere, you only need to create the source storage resources or NAS servers on the storage system. Unisphere does not allow you to create a session with an existing destination. A DR_ is concatenated onto the resource name for local destinations to ensure that the source and destination names on the same system are unique (that is, LUN names need to be unique).

    Note the following:

    • For a disaster recovery scenario, it is recommended that the destination storage resource and NAS server are configured on a storage pool other than the pool used for the source storage resource and NAS server.
    • For a migration scenario, which means migrating the source storage resource and NAS server to a destination storage resource and NAS server on the same pool, use the CLI to configure local replication. The Unisphere GUI does not allow local replication between storage resources and NAS servers on the same pool.

    Configure asynchronous replication

    Before you begin

    If you are configuring asynchronous replication for a tenant, create a pool for the tenant on the destination system that matches the corresponding pool on the source system (if one exists). Then add the tenant to the destination system, using the same UUID and VLANs as the tenant on the source.

    If you are configuring asynchronous replication in a coexisting synchronous and asynchronous replication topology, create the asynchronous replication destination NAS server with both the -replDest and the -backupOnly attributes set to yes. These attributes must be set to yes on the asynchronous replication destination NAS server when the source NAS server is synchronous replicated; otherwise, the asynchronous replication session cannot be created.

    Procedure
    1. Configure the replication interfaces on each SP of the source and destination systems.
    2. Configure a replication connection using the Asynchronous connection mode.
    3. For file storage, create a replication session for the NAS server associated with the file storage.
      Storage resources included in a NAS server automatically get replicated when a replication session is first configured for the NAS server. The replication session for the storage resources will inherit the same attributes as the associated replication session of the associated NAS server. For the storage resources you do not want participating in replication, you can choose to remove the associated replication sessions manually.
    4. Create a remote replication session for the storage resource.
      You only need to configure replication interfaces and connections for the first replication session between two systems. The same connection can be used again for subsequent replication sessions between the same systems.

    Configure synchronous replication

    Only remote replication is supported for synchronous replication.
    Procedure
    1. Identify the Synchronous Replication Fibre Channel (FC) ports on each system.

      To determine the FC port used for synchronous replication, in the CLI console, run the command /remote/sys show -detail. Port information, similar to the following example, will appear in the output:

                                    Synchronous FC ports = spb_fc4, spa_fc4
                                  

      For more information, see the Unisphere CLI User Guide.

    2. Zone the Synchronous Replication FC ports between the systems.
      If the source and destination systems are co-located, instead of zoning, you can choose to use direct-connected FC cables between the SPs.
    3. Configure the replication interfaces on each SP of the source and destination systems based on the connection mode you want:
      • For synchronous replication support (Synchronous connection mode), use the Synchronous Replication Management Ports on each SP of both the systems.
      • For asynchronous and synchronous replication support (Both connection mode), in addition to the replication interfaces for Synchronous Replication Management Ports, configure additional interfaces using the Ethernet Ports on each SP of the source and destination systems.
    4. Configure the replication connection between source and destination systems from the source system only.
      • For synchronous replication support, specify the Synchronous connection mode.
      • For asynchronous and synchronous replication support, specify the Both connection mode.
    5. Create the synchronous replication session.
      You only need to configure replication interfaces and connections for the first replication session between two systems. The same connection can be used again for subsequent replication sessions between the same systems.

    Configure asynchronous replication of synchronous replication to a third site

    Before you begin

    To configure coexisting synchronous and asynchronous replication, the following preconditions must exist:

    1. The source Unity system and two remote Unity systems with OE version 4.4 or later should be installed and powered on.
    2. A zoned Fibre Channel connection exists between the source system and the remote synchronous replication destination system.
    3. IP connections exists between the source and two remote systems.
    4. Each system should have sufficient storage available.
    Only remote replication is supported for synchronous replication.
    Procedure
    1. Create a synchronous replication management interface between the source system and the remote synchronous replication destination system.
    2. Create remote systems to establish a synchronous replication connection between the source system and the synchronous replication destination system.
      The connection mode must be set to Both.
    3. Create asynchronous replication IP interfaces on the source system and the remote destination systems.
    4. Create remote systems to establish asynchronous replication connections between the source system and the asynchronous replication destination system and the synchronous replication destination system and the asynchronous replication destination system.
      The connection mode must be set to Asynchronous.
    5. Create a NAS server on the source system.
    6. Create file systems on the NAS server on the source system.
    7. Create a NAS server synchronous replication session on the source system.
      You only need to configure replication interfaces and connections for the first replication session between two systems. The same connection can be used again for subsequent replication sessions between the same systems.
    8. Create synchronous replication sessions for the file systems on the NAS server on the source system.
      Storage resources included in a NAS server automatically get replicated when a replication session is first configured for the NAS server. The replication session for the storage resources will inherit the same attributes as the associated replication session of the associated NAS server.
    9. Create a NAS server asynchronous replication session on the source system.
      The asynchronous replication destination NAS server is selected as Used as backup only in Unisphere by default when synchronous replication is already enabled. When using CLI, it must be specified, otherwise, the asynchronous replication session creation will fail.
    10. Create asynchronous replication sessions for the file systems on the NAS server on the source system.
      Storage resources included in a NAS server automatically get replicated when a replication session is first configured for the NAS server. The replication session for the storage resources will inherit the same attributes as the associated replication session of the associated NAS server.

    Replication interfaces

    Each SP must include at least one replication interface configured on it. Each replication interface on the SP of the source system should be able to communicate to the replication interface on the SP of the destination system. To establish this, you must set up a switched network for remote replication. You can configure a replication interface with an IPv4 or IPv6 address.

    Replication is supported between like type IP addresses. For example, you can set up a replication connection between a replication interface configured with IPv4 address on the source system and a replication interface configured with IPv4 address on the remote system.

    Configuration for asynchronous replication

    When you create replication interfaces for asynchronous replication, use any of the available Ethernet ports to configure an IP address on each SP. These IP addresses are then used for asynchronous replication between the remote systems.

    Configuration for synchronous replication

    When you create replication interfaces for synchronous replication, you must use the Ethernet Port titled 'Sync Replication Management Port' to configure an IP address on each SP. This port is specifically used for management of the synchronous replication session, leveraging the same physical interface as the storage system's Unisphere management port, whereas the Fibre Channel (FC) ports are used for replicating data between systems. Before creating replication interfaces and connections for synchronous replication, ensure that you complete FC zoning and configuration.

    You can choose to configure Asynchronous, Synchronous, or both connection modes for block storage resources. If you choose to configure both connection modes, ensure that you configure an additional Ethernet Port IP interface on each SP of the source and destination systems.

    About replication connections

    Replication requires a configured connection between the source system and destination system. This connection is called a replication connection. Replication connections use replication interfaces on each SP from the local system and pairs them up with the replication interfaces on each SP in the remote system.

    For synchronous replication, a Fibre Channel (FC) connection is required for the data communication, and an IP interface for the management communication. Only one FC port can be configured and used for synchronous replication. Once an FC port is assigned, it will continue to act as the synchronous replication port and can never be changed.

    To determine the FC port used for synchronous replication, in the CLI console, run the command /remote/sys show -detail. Port information, similar to the following example, will appear in the output:

                        Synchronous FC ports = spb_fc4, spa_fc4
                      

    For more information, see the Unisphere CLI User Guide.

    Before creating a replication interface or connection for synchronous replication, it is recommended that you configure the FC zoning.
    Connection modes

    The following connection modes are supported:

    • Asynchronous—Supports asynchronous replication of file and block storage resources. It uses the Ethernet Port IP interfaces configured on Storage Processor A (SP A) and Storage Processor B (SP B) on the source and destination systems. Manual replication uses asynchronous connection as well.
    • Synchronous—Supports synchronous replication of file and block storage resources. It uses the Sync Replication Management Port with IP addresses configured on SP A and SP B on the source and destination systems.
    • Both—Supports synchronous replication of file and block storage resources using the Sync Replication Management Port and asynchronous replication of file and block storage resources. Ensure that you set up the additional Ethernet Port IP interfaces on SP A and SP B on the source and destination systems.

    About replication sessions

    A replication session leverages a configured replication connection and associated interfaces to establish an end-to-end path for replicating data between the source and destination storage resources. For asynchronous replication, once a replication session is established, the system creates two replication system snapshots on the source storage resource and two replication system snapshots on the destination storage resources. The snapshots are used to keep point-in-time copies of data and maintain a common base between the source and destination storage resources.

    The snapshots are refreshed based on the replication mode:

    • For automatic synchronization, the snapshots are refreshed based on the Recovery Point Objective (RPO) you specified. You can adjust the RPO interval based on the amount of protection you want.
      For asynchronous replication, you can specify an RPO from a minimum of 5 minutes up to a maximum of 1440 minutes (24 hours). Once set, the RPO value cannot be reset from non-zero (for asynchronous replication) to zero (the automatic static setting of RPO for synchronous replication) or from zero to non-zero.
    • For manual synchronization, it is recommended that you synchronize the replication periodically.
    The snapshots consume protection space based on the snapshots feature. Although the internal snapshots may appear listed in the Snapshots tab of a storage resource (source or destination), you cannot manage or modify them. The snapshots also do not participate in automatic delete operations.

    The following steps provide a high level overview of how the asynchronous replication session works:

    1. When the session and the internal snapshots are created, an initial synchronization occurs where all the data from the first snapshot of the source storage resource is replicated to the destination storage resource.
      For automatic synchronization, initial synchronization is enabled by default. For manual synchronization, there is no initial synchronization. An option is available for asynchronous replication to replicate existing snapshots on the storage resource as part of the initial synchronization. This option is only available when creating a replication session. In this case, replication transfers the snapshots in the order in which they were created on the source to the destination site. If you opt not to synchronize existing snapshots as part of the initial synchronization, the replication copies only the source data from the internal system snapshot.

      The system supports up to 16 concurrent initial synchronization operations per SP.

    2. Once data is replicated to the destination storage resource, the first snapshot on the destination storage resource is refreshed.

      The first snapshot on both systems then becomes your common base at that point in time. In event of a disaster, the common base is used to restore data from the last time it was synchronized.

    3. When the session is synchronized next, manually or automatically (based on the RPO), the second internal snapshot on the source system gets refreshed.
      If a replication session is created with auto synchronization, any snapshots created or marked for replication since the previous RPO are replicated upon RPO expiry to the destination site. In case of a session configured with manual synchronization, any snapshots created or marked for replication since the last synchronization occurred are replicated whenever the session is manually synchronized.
    4. Once the snapshot is refreshed, data is replicated to the destination storage resource.
      Only the differential data between the first and second snapshots gets copied over.
    5. The second snapshot on the destination storage resource is then refreshed.
    6. Once this occurs, at that point-in-time, the second snapshots on both the systems now become the common base.

    These steps occur each time a synchronization occurs. When a disaster occurs, replication uses the common base to go back to a good point in time copy of data. If failing over to the common base is not sufficient and replicated user snapshots exist, manually restore the destination resource to any of the replicated user snapshots.

    Synchronous file replication works differently than asynchronous file replication. Once the operational status of a synchronous file replication session is Active, checkpoint snapshots that are created on the source system (either manually through Unisphere, CLI, RESTful command, or by a snapshot schedule) are synchronously created on the destination system. Snapshots that were created before the synchronous replication session was setup are not replicated.

    For synchronous replication, the RPO is set to 0 automatically and the NAS server configuration is synchronously replicated to the destination system so that after failover, the destination NAS server can reflect the latest configuration. However, the view of the NAS server configuration at the destination system from the management interface is not always up to date, it is only updated automatically every 15 minutes. An on demand update of the view of the NAS server configuration at the destination system can be issued from either Unisphere (Refresh Configuration) or CLI (net/nas/server {-id <value> | -name <value> update -confView}). Since the synchronous replicated configuration file system is unreadable during initial synchronization or synchronizing after a fracture, it is not possible to update the view of the NAS server configuration at the destination side at those times.

    About replication support for thin storage resources with data reduction

    A thin destination LUN or LUN Group can be created with data reduction during replication session creation when the following criteria is met:

    • The source LUN or LUN group is thin.
    • The OE version is 4.2 or later.
    • The pool is All-Flash.

    If the source LUN or LUN group meet this criteria, thin is selected by default for the destination LUN or LUN group. You can choose to unselect it to create a thick destination LUN or LUN group. If thin is not selected for the destination storage resource, data reduction cannot be selected. Data reduction can only be selected when thin can be and is selected for the destination storage resource.

    For file systems, replication matches the destination storage resource to the source. The destination is converted to match with the source after the synchronization operation (initial synchronization or manual synchronization). Therefore in this case, thin and data reduction cannot be selected.