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Since historical data is one of the most valuable items in SCADA and MES systems, the archive process is one of the first to be configured as redundant. On two (or more) computers, a pair of watchdog + D2000 Archiv processes is configured using the SCS Config utility with the parameter /W<name>,<instance> indicating the name and number of the instance (e.g. /WSELF,1 or /WSELF,2) and with the parameter /S, /RD, or /RF specifying the server or redundancy group to which the archive connects (see Starting user processes).
Each of the instance archive processes instances archives the same historical values (children of SELF.ARC). The D2000 Server process controls which instance is active (to which read requests are directed). Other instances are passive.
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The Arcsynchro utility, which D2000 Archive Archiv can run automatically at startup (see the ArcsynchroAuto archive parameter), is used to synchronize data between archives (patching a hole after a failure of one of the instance archives or migrating archive data between different SQL databases).
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