What Is the Usage of the Secondary LUN of a Remote Replication

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In a remote replication, the secondary LUN and the primary LUN form a pair, and the secondary LUN backs up data on the primary LUN.
? In normal cases, the secondary LUN of a remote replication cannot be accessed by hosts. Therefore, if a host needs to access a secondary LUN, you can create a snapshot for the secondary LUN and map the snapshot to the host for access.
? In the event that a primary LUN failed, which leads to service interruption, you must perform a primary/secondary switchover to switch the secondary LUN to the primary LUN and then map the new primary LUN to the host for data access.

Other related questions:
What Is the Usage of the Secondary LUN of Remote Replication?
In a remote replication session, the secondary LUN and the primary LUN form a pair, and the secondary LUN backs up the data on the primary LUN. Normally, the secondary LUN (unreadable and unwritable) cannot be accessed by hosts. If a host needs to access the secondary LUN, you can create a snapshot for the secondary LUN and map the snapshot to the host.

How to use a secondary LUN in a remote replication?
In a remote replication, the secondary LUN and the primary LUN form a pair, and the secondary LUN backs up data on the primary LUN. ? By default, the secondary LUN cannot be accessed (read or written) by a host. If a request is made to access data on the secondary LUN, you can create a virtual snapshot for the secondary LUN, and then map the virtual snapshot to the host for access. ? When a primary LUN encounters a critical error and the services are interrupted, you must perform the master/slave switchover to switch the secondary LUN to the primary LUN, and then map the new primary LUN to the host for access. NOTE: For details on how to perform a master/slave switchover, choose Help > Help Topics on the ISM, and view the related help information.

What Is the Difference Between Synchronous Remote Replication and Asynchronous Remote Replication
Both synchronous remote replication and asynchronous remote replication can be used in disaster recovery solutions implemented by storage systems to back up data remotely. However, they are implemented in different ways and applicable to different service scenarios. Implementation modes are describes as follows: ? Synchronous remote replication: When a host writes data to the primary LUN, a write request is also sent to the secondary LUN. After both LUNs return a response indicating a successful I/O write, the primary storage system sends the host a response indicating a successful I/O write, implementing real-time data synchronization between the primary LUN and the secondary LUN. ? Asynchronous remote replication: When writing data to the primary LUN, the primary storage system records the changed data. After the primary LUN returns a response indicating a successful write, the primary storage system sends the host a response indicating a successful write. Then, data synchronization is triggered by a user manually or by the system based on user-defined trigger conditions to ensure data consistency between the primary LUN and the secondary LUN. Service scenarios are described as follows: ? Synchronous remote replication requires high bandwidth and low data latency. Therefore, synchronous remote replication is typically used in disaster recovery scenarios where the primary and secondary storage systems are adjacent to each other, such as the intra-city data backup and disaster recovery scenario. ? Asynchronous remote replication is not demanding on bandwidth and data latency. Therefore, asynchronous remote replication is applicable to disaster recovery scenarios where the primary and secondary storage systems are far away from each other or the network bandwidth is limited.

What is the relationship between NAS remote replication and SAN asynchronous remote replication?
The N8500 NAS remote replication is implemented based on SAN asynchronous remote replication. Each N8500 NAS remote replication pair corresponds to a consistency group of SAN asynchronous remote replication. If any resource in the consistency group of SAN asynchronous remote replication is faulty, the N8500 NAS remote replication become invalid as well. Then the storage unit will generate an alarm. You can rectify the fault according to the suggested actions in the alarm.

What is the principle of setting bandwidth for remote replication and LUN copy among storage arrays?
The bandwidth refers to the amount of data that is transferred on a channel in a certain period of time. Its common unit is bit per second (bps). The bandwidth of a computer network refers to the maximum data rate on the network, namely, the number of bits transferred per second. When setting the bandwidth, note the following: ? The bandwidth should be set to meet the requirements of actual services. You can customize a proper bandwidth as required. ? The bandwidth should be set no larger than the current bandwidth of customers' network. If the workload in the system is heavy, the bandwidth for remote replication and LUN copy among storage arrays can be correspondingly reduced to guarantee the normal running of ongoing services.

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