VMware VCENTER SERVER 4.0 - GETTING STARTED UPDATE 1 Specifications download pdf (Page 17)

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Chapter 1 Introduction

Failover Process

Figure 1-6. Failover

When the passive server detects the active server is no longer running properly, it assumes the active server

role by taking the following steps.

1 The server applies any intercepted updates that are currently saved in the passive server (safe) update

queue, that is, the log of update records saved on the passive server but not yet applied to the replicated

files.

The length of the passive server (safe) queue affects the time the failover process takes to complete. If the

passive server queue is long, the system must wait for application of all passive server updates before the

rest of the process can take place.

When no more update records can be applied, any update records that the server was unable to apply are

discarded. An update record can only be applied if all earlier update records were applied and the

completion status for the update is in the passive server (safe) update queue.

2 The server switches its role from passive to active.

The server enables the public identity of the server. The active and passive servers both have the same

system name and same Principal (Public) IP address. This Principal (Public) IP address can be enabled on

only one of the two systems at a time. When the public identity is enabled, any clients connected to the

server before the failover can now reconnect.

3 The server starts intercepting updates to the protected data. Updates to the protected data are saved in

the active server (unsafe) update queue.

4 The server starts all the protected applications. The applications use the replicated application data to

recover before allowing clients to reconnect. Any updates that the applications make to the protected data

are intercepted and logged.

At this stage, the originally active server is offline, and the originally passive server has taken over the active

server role and is running the protected applications. Because the originally active server stopped abruptly,

the protected applications possibly lost some data, but the no synchronization mode update that completed

before the failover is lost. The application clients can reconnect to the application and continue running as

before.

During a failover, the data in the active server (unsafe) queue is lost.

Recovery from a Failover

Assuming that the active server before the failover was the Primary server, and the Secondary server has

assumed the active role following a failover, you can reinstate the Primary server to an active role after

rectifying the problem that initiated the failover.

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VMware VCENTER SERVER 4.0 - GETTING STARTED UPDATE 1 Specifications Page 17