The steps that are taken during the synchronization process differ depending on whether Duty Mode is enabled or disabled on the servers, by default the Duty Mode setting is disabled.
Once a ‘First pass’ synchronization is complete, the Main server continues to update the Standby server on a regular basis. These regular updates are called ‘Short passes’ as they usually take less time to complete than a ‘First pass’ (as the Main server only has to update the Standby server with new data, not all data).
‘Short passes’ take place continuously, the frequency of the ‘short passes’ is defined by the Transfer Interval and Interleave settings on the Server Configuration Tool (though it is possible for ‘short passes’ to be delayed).
During a ‘Short pass’ the Main server checks for any changes to the following and transfers them to the Standby server:
- The database structure, this includes the hierarchy of groups, items and so on.
- Configuration changes.
- The saved data or dynamic data.
- Updates to the alarm or event data.
- New historic records that have been created on the Main server. Any historic record that is on the Main server but, has not yet been transferred to the Standby server is regarded as ‘new’.
- If there are new historic records, at least 1 of them has to be transferred during a ‘Short pass’ (the next ‘Short pass’ cannot occur until at least 1 historic record has been transferred).
- New event records that have been created.
In addition the Main server transfers the historic files (generated reports) to the Standby server.
If the Standby server is not fully synchronized with the Main server by the time the next ‘short pass’ is due, the current ‘short pass’ is ended and the next ‘short pass’ takes place. The only exception to this rule is if there are new historic records to be transferred, but no historic records were transferred during the ‘short pass’. In this situation, the next ‘short pass’ is delayed until at least 1 historic record has been transferred.
Example:
The Main server has new historic records that need to be transferred to the Standby server during a ‘short pass’. The Transfer Interval has been set to 2 seconds and the Interleave is 1. The ‘short pass’ begins, but after 2 seconds, it has yet to transfer any historic records. The next ‘short pass’ is due to start, but as no new historic records have been transferred, it has to be delayed. A further second passes and 1 historic record is transferred. With 1 historic record transferred, the ‘short pass’ can end and the next ‘short pass’ can begin (1 second later than expected).
Further Information