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Remote Replication Feature Guide for File 04

OceanStor 5300 V3, 5500 V3, 5600 V3, 5800 V3, and 6800 V3 Storage System V300R002

"This document describes the file system remote replication feature, in terms of the implementation principle,application scenario, and explains how to configure and manage this feature."
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Related Concepts

Related Concepts

This section describes concepts related to the remote replication feature, including pair, synchronization, splitting, primary/secondary switchover, data status and writable secondary file system.

Full implementation of remote replication consists of five phases: creating a remote replication pair, replicating data, switching services, restoring data, and restoring the pair, as shown in Figure 1-1.
Figure 1-1  Implementation of remote replication

NOTE:
As the ID of local authentication user is local data, the information of local authentication user can not be replicated.

Pair

A pair refers to the relationship between a primary file system and a secondary file system of a remote replication session. In a pair, data can be replicated only from the primary file system to the secondary file system. People can speak over two phones only after a connection is set up between the phones by dialup. Similarly, data can be replicated from the primary file system to the secondary file system only after a pair is set up between the file systems. The primary and secondary file systems of a pair must come from different storage systems.

A pair may be in different running status at different phases of a remote replication session. By viewing the running status of a pair, you can determine whether you need to perform an operation for that pair, and what operation should be performed if you need. After you perform an operation, you can view the pair running status to determine whether the operation succeeded. Table 1-3 describes the pair running status involved in a remote replication session.
Table 1-3  Pair running status of a remote replication session

Running Status

Description

Normal

Data synchronization between the primary file system and the secondary file system is complete.

Split

Data replication between the primary file system and the secondary file system is suspended. The pair running status changes to Split after the primary and secondary file systems are split from each other manually by the administrator.

Interrupted

The pair running status changes to Interrupted after the pair between the primary and secondary file systems is interrupted because the links used by the remote replication are interrupted or any of the two file systems fails.

To be recovery

If a remote replication session needs to be restored using a Manual policy after the fault that caused a pair interruption is removed, the pair running status changes to To be recovery. This status reminds users of manual synchronization between the original primary file system and the secondary file system to restore the pair.

Invalid

If the original basic pair properties of the primary or secondary file system are changed (for example, the secondary file system configured at the secondary site is deleted) after the pair is interrupted, configuration becomes inconsistent between the primary and secondary sites and the pair running status changes to Invalid.

Synchronizing

Data is being copied from the primary file system to the secondary file system. When a pair is in this state, data on the secondary file system is unusable.

Synchronization

Synchronization refers to the process during which data is copied from the primary file system to the secondary file system. When data is inconsistent between the primary file system and secondary file system, you can manually synchronize data from the primary file system to the secondary file system to ensure data consistency.
NOTE:

During synchronization, the storage system synchronizes the expiration time and WORM clock information of the file system. The updated values can be queried in the secondary file system only after the remote replication is deleted.

Splitting

If you want to suspend the remote replication relationship of a pair when analyzing data and recording reports, you can split the pair to suspend data synchronization without affecting data of the primary file system.

Splitting refers to the action of stopping data replication from the primary file system to the secondary file system. After the splitting, the pair relationship between the primary file system and the secondary file system still exists and the access permission of hosts for the primary and secondary file systems remains unchanged.

Users can effectively control a remote replication process by performing synchronization and splitting.

Primary/Secondary Switchover

A primary/secondary switchover is a process during which the primary and secondary file systems in a pair exchange their roles. A primary/secondary switchover changes the original relationship between the file systems in a remote replication session (a new pair is formed). You can perform a primary/secondary switchover for a single remote replication session. Usually, a primary/secondary switchover is performed in the following scenarios:
  • Data is synchronized from a backup site to a production site. After the production site takes over services, a primary/secondary switchover is performed again. Data is synchronized from the production site to the backup site.
  • When the primary storage system needs to be upgraded and maintained and the secondary file system is required to take over services, an administrator performs a primary/secondary switchover at the primary or secondary site.

After a primary/secondary switchover, services are running on the secondary storage system. Therefore, it is required that data on the secondary file system is available before a primary/secondary switchover is initiated. You can determine whether data on the secondary file system is available by viewing the data status of the secondary file system.

Data Status

The remote replication feature identifies the data status of the current pair by determining whether data of the secondary file system is available at a specific point in time. If a disaster occurs, the remote replication feature determines whether to allow a primary/secondary switchover for a pair based on the data status of the pair. There are two pair data states: Consistent and Inconsistent.

Readable and Writable Secondary File System

The secondary file system can receive data from hosts, and its data can be read by hosts. By default, the secondary file system cannot be read and written after remote replication is configured. If the primary file system fails, an administrator click Disable Protection for Secondary Resource and manually set the secondary file system to writable and readable. In this way, the secondary storage system can take over host services, ensuring service continuity. The secondary file system must be readable and writable in the following two scenarios:
  • The primary file system fails and the remote replication link is disconnected. The secondary file system must be set to readable and writable in the secondary storage system.
  • The primary file system fails and the remote replication link is normal. The pair must be split and then the secondary file system must be set to readable and writable in the primary or secondary storage system.
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Updated: 2019-01-02

Document ID: EDOC1000069276

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