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OceanStor 2600 V3 Storage System V300R005 HyperMetro Feature Guide 06

"This document describes the implementation principles and application scenarios of theHyperMetro feature. Also, it explains how to configure and manage HyperMetro."
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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 adopts an arbitration mechanism to determine priorities of services in 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 third-place quorum servers are deployed.
NOTE:

The quorum server mode is recommended. After a quorum server is deployed, the non-preferred site of HyperMetro will automatically take over services once the preferred site becomes faulty, without causing HyperMetro service interruption.

Types of Faults in Static Priority Mode

The Static Priority Mode applies to scenarios where no third-place quorum server is deployed.

  • If the link between the two storage arrays in the two data centers or the storage array at the non-preferred site breaks down, LUNs of the storage array at the preferred site continue providing services for hosts but LUNs of the storage array at the non-preferred site stop providing services for hosts.
  • If the storage array at the preferred site breaks down, the storage array at the non-preferred site cannot automatically take over HyperMetro services from the storage array at the preferred site. As a result, HyperMetro services stop. In this case, you must forcibly start the storage array at the non-preferred site to provide services for hosts.
NOTE:

When you use OceanStor DeviceManager or CLI to power off a storage device, the storage device will notify the peer storage device of taking over services. This event is not a device fault.

In a HyperMetro pair, you can set one data center as a preferred site and the other data center as a non-preferred site. In the following example, data center A is used as a preferred site. Table 1-1 lists the types of faults in Static Priority Mode.

NOTE:

After the HyperMetro pair fails, you can set Recovery Policy by Modifying HyperMetro Pair Properties.

  • Automatic: The system automatically performs the synchronization operation for data recovery.
  • Manual: The synchronization operation must be performed manually for data recovery.
Table 1-1 Types of faults in static priority mode

No.

Fault Diagram

Fault Type

HyperMetro Pair Running Status

Arbitration Result

1

The link between two storage arrays breaks down.

To be synchronized

The LUN in data center A continues providing services but the LUN in data center B stops providing services.

2

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

To be synchronized

The LUN in data center A continues providing services but the LUN in data center B stops providing services.

3

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

To be synchronized

The LUN in data center A loses efficacy and the LUN in data center B stops providing services. You must forcibly start the LUN in data center B to enable the LUN to provide services for hosts.

Black cable: Indicates HyperMetro replication network.

Types of Faults 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 center. If the storage array in one data center crashes or the link between two storage arrays is down, the storage array in each data center sends an arbitration request to the quorum server. The storage array that wins the arbitration continues providing services but the storage array that fails in the arbitration stops providing services. The preferred site takes the precedence in an arbitration.

The quorum server provides different arbitration results depending on fault scenarios. In a HyperMetro pair, you can set one data center as a preferred site and the other data center as a non-preferred site. Data center A is used as a preferred site. Table 1-2 lists the types of faults in Quorum Server Mode.

NOTE:

After the HyperMetro pair fails, you can set Recovery Policy by Modifying HyperMetro Pair Properties.

  • Automatic: The system automatically performs the synchronization operation for data recovery.
  • Manual: The synchronization operation must be performed manually for data recovery.
Table 1-2 Types of faults in quorum server mode

No.

Fault Diagram

Fault Type

HyperMetro Pair Running Status

Arbitration Result

1

The quorum server breaks down.

Normal

In a HyperMetro pair, the LUNs in data center A and data center B continue providing services.

NOTE:

The arbitration mode of HyperMetro automatically becomes the priority mode.

2

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

Normal

In a HyperMetro pair, the LUNs in data center A and data center B continue providing services.

3

One storage array malfunctions.

To be synchronized

In a HyperMetro pair, the LUN in data center A loses efficacy but the storage array in data center B continues providing services.

4

The link between two storage arrays breaks down.

To be synchronized

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

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

NOTE:

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

5

Both one storage array and the quorum server malfunction.

To be synchronized

In a HyperMetro pair, the LUN in data center A loses efficacy and the LUN in data center B stops providing services.

NOTE:

You must start the LUN in data center B to enable the LUN to provide services for hosts.

6

Both the link between two storage arrays and the link between one storage array and the quorum server are down.

To be synchronized

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

7

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

To be synchronized

In a HyperMetro pair, the LUN in data center A loses efficacy and the LUN in data center B stops providing services.

NOTE:

You must start the LUN in data center B to enable the LUN to provide services for hosts.

8

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

To be synchronized

Result 1: If the quorum server fails, the link between storage systems is interrupted, and the interval between the two faults exceeds 60 seconds, the arbitration result is that LUNs in data center A continue providing services and LUNs in data center B stop providing services.

Result 2: If the quorum server fails, the link between storage systems is interrupted, and the interval between the two faults is within 60 seconds, the arbitration result is that LUNs in both data center A and data center B stop providing services. You must manually start LUNs in either data center to provide services.

9

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

Normal

In a HyperMetro pair, the LUNs in data center A and data center B continue providing services.

NOTE:

The arbitration mode of HyperMetro automatically becomes the priority mode.

Black cable: Indicates HyperMetro replication network.

Green cable: Indicates quorum network.

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Updated: 2018-09-03

Document ID: EDOC1000106183

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