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FusionStorage V100R006C30 Block Storage Service Disaster Recovery Feature Guide 03

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Arbitration Mechanism

Arbitration Mechanism

If the link between two data centers breaks down, data cannot be synchronized between the two data centers and only one data center continues providing services. To ensure data consistency, HyperMetro uses an arbitration mechanism to determine the service priority of data centers.

HyperMetro supports two arbitration modes:
  • Static Priority Mode: Applies to scenarios where no third-place quorum server is deployed.
  • Quorum Server Mode: Applies to scenarios where a third-place quorum server is deployed. In this mode, an independent physical server or a VM is used as the quorum server. You are advised to deploy the quorum server at a third-place site to prevent the server faults occurred in the event of a data center disaster.

Arbitration Policies in Static Priority Mode

Static Priority Mode applies to scenarios where no third-place quorum server is deployed.
  • If the link between the two storage systems is down or the storage system at the non-preferred site becomes faulty, volumes in the storage system at the preferred site continue providing services for hosts but volumes in the storage system at the non-preferred site stop providing services for hosts.
  • If the storage system at the preferred site is not working normally, the storage system at the non-preferred site cannot automatically take over HyperMetro services from the storage system at the preferred site. As a result, HyperMetro services stop, and you need to forcibly start the storage system at the non-preferred site to provide services for hosts.
In a HyperMetro pair, you can set one data center as the preferred site and the other as the non-preferred site. In the following example, data center A is used as the preferred site. Table 1-2 lists the arbitration policies in Static Priority Mode.
Table 1-2  Arbitration policies in Static Priority Mode

No.

Fault Diagram

Fault Type

HyperMetro Pair Running Status

Arbitration Result

1



The link between two storage systems breaks down.

To Be Synchronized

In a HyperMetro pair, the volume in data center A continues providing services but the volume in data center B stops providing services.

2



The storage system in data center B (non-preferred site) malfunctions.

To Be Synchronized

In a HyperMetro pair, the volume in data center A continues providing services but the volume in data center B stops providing services.

3



The storage system in data center A (preferred site) malfunctions.

To Be Synchronized

In a HyperMetro pair, the volume in data center A becomes invalid and the volume in data center B stops providing services. You need to forcibly start the volume in data center B to provide services for hosts.

Black cable: Indicates the HyperMetro replication network.

Arbitration Policies in Quorum Server Mode

In Quorum Server Mode, you can determine whether the storage systems work properly based on the heartbeats between storage systems in the data centers. If the storage system in one data center fails or the link between two storage systems is down, the storage system in each data center applies for arbitration to the quorum server. The storage system that wins the arbitration continues providing services, whereas the storage system that fails the arbitration stops providing services. The preferred site takes precedence in the arbitration.

In a HyperMetro pair, you can set one data center as the preferred site and the other as the non-preferred site. In the following example, data center A is used as the preferred site, and the quorum server provides different arbitration results depending on fault scenarios. Table 1-3 lists the arbitration policies in Quorum Server Mode.
Table 1-3  Arbitration policies in Quorum Server Mode

No.

Fault Diagram

Fault Type

HyperMetro Pair Running Status

Arbitration Result

1



The quorum server becomes faulty.

Normal

In a HyperMetro pair, both volumes in data center A and data center B continue providing services.

NOTE:

The HyperMetro arbitration mode automatically switches to Static Priority Mode.

2



The link between one storage system and the quorum server breaks down.

Normal

In a HyperMetro pair, both volumes in data center A and data center B continue providing services.

3



One storage system malfunctions.

To Be Synchronized

In a HyperMetro pair, the volume in data center A becomes invalid and the volume in data center B continues providing services.

4



The link between two storage systems breaks down.

To Be Synchronized

Result 1: In a HyperMetro pair, the volume in data center A continues providing services but the volume in data center B stops providing services.

Result 2: In a HyperMetro pair, the volume in data center B continues providing services but the volume in data center A stops providing services.

NOTE:

As the preferred site, data center A has the arbitration priority. Generally, the arbitration result is Result 1.

5



One storage system and the quorum server malfunction.

To Be Synchronized

In a HyperMetro pair, the volume in data center A becomes invalid and the volume in data center B stops providing services.

NOTE:

You need to manually start the volume in data center B to provide services for hosts.

6



The link between two storage systems and the link between one storage system and the quorum server are down.

To Be Synchronized

In a HyperMetro pair, the volume in data center A stops providing services but the volume in data center B continues providing services.

7



One storage system malfunctions and the link between the other storage system and the quorum server is down.

To Be Synchronized

In a HyperMetro pair, the volume in data center A becomes invalid and the volume in data center B stops providing services.

NOTE:

You need to manually start the volume in data center B to provide services for hosts.

8



The quorum server malfunctions and the link between two storage systems is down.

To Be Synchronized

Result 1: In a HyperMetro pair, the quorum server fails. Then the link between storage systems is interrupted. If the interval between the two faults exceeds 20 seconds, the arbitration result is that the volume in data center A continues to provide services and the volume in data center B stops providing services.

Result 2: In a HyperMetro pair, the quorum server fails. Then the link between storage systems is interrupted. If the interval between the two faults is within 20 seconds, the arbitration result is that both volumes in data centers A and B stop providing services. You need to manually start the volume in data center A or B to provide services for hosts.

9



The quorum server malfunctions and the link between the quorum server and one storage system is down.

Normal

In a HyperMetro pair, both volumes in data center A and data center B continue providing services.

NOTE:

The HyperMetro arbitration mode automatically switches to Static Priority Mode.

Black cable: Indicates the HyperMetro replication network.

Green cable: Indicates the arbitration network.

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Updated: 2019-01-17

Document ID: EDOC1100044928

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