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Technical Article | TA-20201002-TP-36 VDG Sense | Tutorials | Failover  | PDF Download |
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Introduction
A ’Failover’ server, or ’Hot Standby’ server is used to monitor one or more servers in the same installation. The failover server actively checks if the monitored servers are still functioning. When it detects a server is not responding anymore, it will automatically take-over the server using the same settings of the ’failed’ server, thus emulating its configuration. When the original server is back online, the failover server will shutdown automatically.
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The Failover server will use the following default timeout values to indicate if the failover procedure should be started:
Type | Default Timeout value | Description |
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Connected | 5 minutes | A network connection has been made, but the first startup message has not been received |
Started | 5 minutes | The startup message has been received, but the first keep-alive message has not been received |
Keep alive | 30 seconds | No new keep-alive message is received |
Normal shutdown | 15 minutes | The server has been shutdown normally, but has not restarted yet |
Abnormal shutdown | 5 minutes | The server has exited with an error and has not restarted yet |
The values can be modified in the failover settings.
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For example, camera channels are set to max 10 days of recording and during the first three days monitored server failed and the failover server was storing video:
Date (day) | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 |
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Storage duration | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 |
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Data on original server | F | F | F | S | S | S | S | S | S | S | W |
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Data on failover server | S | S | S |
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S:Stored, F:Failed, D:Deleting, W:Writing
The server is constantly checking if the maximum storage duration is reached. This means that on day 11-14 it starts deleting videodata on the failover server:
Date (day) | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 |
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Storage duration |
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| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 |
Data on original server | F | F | F | D | S | S | S | S | S | S | S | S | S | W |
Data on failover server | D | D | D |
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S:Stored, F:Failed, D:Deleting, W:Writing
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