Resolving MIS Server Daily Report Failures During Redundant OS Server Switchover

Management Information System (MIS) daily report generation failures occurring when a redundant standby OS server assumes the Master role are caused by hardcoded database connection strings, unsynchronized SQL archive tables, or mismatched SQL Server service permissions. External reporting platforms—such as WinCC Information Server, DataMonitor, or custom SQL reporting engines—must target the redundant server pair name rather than a static physical computer name. Additionally, if the WinCC Redundancy internal synchronization fails, the standby server lacks historical data required to build daily reports. Resolving this requires configuring redundant OLE-DB connection providers, auditing the WinCC Redundancy archive replication state, and standardizing SQL service account credentials across both servers.

Architecture of Redundant WinCC OS and MIS Integration

In SIMATIC PCS 7 redundant server environments, two paired WinCC OS servers (Server 1 and Server 2) operate in continuous synchronization. An external Management Information System (MIS) or reporting station extracts process values, alarms, and batch logs using Microsoft SQL Server queries, the WinCC OLE-DB Provider, or the WinCC Connectivity Pack.

External clients must not maintain hardcoded TCP/IP connections to a single physical computer. When Server 1 fails or undergoes maintenance, Server 2 dynamically assumes the active Master role. The reporting framework must transparently redirect queries to the currently active Master database or query the Process Historian (PH) central repository.

Root Causes of Switchover Report Generation Failures

Switchover report failures typically originate from three core architecture breakdowns:

Failure MechanismRoot CauseImpact on MIS ReportingStatic Server TargetingMIS configuration references Server1\WinCC instead of the redundant pair or @ServerName.Reports generate successfully when Server 1 is Master; complete report generation failure when Server 2 is Master.Archive Synchronization GapWinCC Redundancy archive synchronization broken or delayed across the redundancy serial/Ethernet link.Server 2 database contains missing tag intervals, causing SQL aggregations (SUM, AVG) to return NULL or abort scripts.SQL Authentication DisparitySQL Server service accounts, Windows domain permissions, or linked server logins differ between Server 1 and Server 2.SQL query authentication rejected by Server 2 when MIS attempts database connection.

Remediation and Connection String Configuration

To establish high-availability reporting across redundant WinCC OS servers:

1. Configure the WinCC OLE-DB Provider for Redundancy

In the MIS reporting tool (e.g., Crystal Reports, Excel VBA, SQL Server Reporting Services), utilize the WinCC OLE-DB Provider with redundant catalog parameters:

Provider=WinCCOLEDBProvider.1;
Catalog=CC_External_Project_Name;
Data Source=Server1\WinCC,Server2\WinCC;
Location=Redundant;

The Location=Redundant parameter instructs the OLE-DB provider to dynamically query the active Master server and automatically redirect SQL queries if Server 1 transitions to standby or offline.

2. Verify WinCC Redundancy Synchronization

Open WinCC Explorer on Server 1 and Server 2:
1. Double-click the Redundancy editor.
2. Ensure the checkboxes for Activate Redundancy, Connection to redundant partner, and Synchronization after return of partner (Alarm Logging, Tag Logging) are fully enabled.
3. In the WinCC Alarm Control, verify that internal system messages Redundancy: Synchronization completed are logged without timeout faults.

3. Align SQL Security Roles

Ensure that the Windows service account running the MIS reporting engine belongs to the SIMATIC HMI group on both Server 1 and Server 2.

Verification

To verify that daily reports generate properly regardless of which server is active Master:

Confirm reports generate successfully while Server 1 is Master.
Simulate a server switchover: On Server 1, deactivate WinCC Runtime or temporarily disconnect the plant bus cable.
Confirm that Server 2 transitions to active Master (@RedundantServerState = 1).
Trigger the MIS daily report generation script manually on the reporting station.
Verify that the SQL query executes without timeout or authentication errors, and that the resulting PDF/Excel report displays complete, continuous trend data without gaps.

Limitations and Operational Precautions

Operational boundaries for redundant reporting:

Tag Logging Fast vs Slow Buffers: If reports query high-resolution archives, ensure Tag Logging Fast data has completed flush to the SQL database before daily query execution.
Avoid Direct SQL Table Writes: The MIS reporting system must strictly execute read-only queries against WinCC SQL views or the WinCC OLE-DB Provider. Never execute INSERT, UPDATE, or DELETE statements on runtime archive tables (*_ALG, *_TLG).
Process Historian Deployment: For enterprise-scale reporting, deploy a dedicated SIMATIC Process Historian (PH) rather than querying live redundant OS runtime servers directly.

Engineer FAQ

Can WinCC Information Server connect to redundant OS servers directly?

Yes. When configuring WinCC Information Server data sources, select the redundant server pair project; Information Server automatically monitors server status and routes queries to the active Master node.

Why do daily reports show NULL values after a redundancy switchover?

NULL values occur if historical archive synchronization between Server 1 and Server 2 was incomplete or stalled, leaving the newly active Master database with gaps in tag logging tables.

What internal WinCC system tag indicates which server is currently Master?

The internal binary tag @RedundantServerState indicates status: 1 indicates Master, 2 indicates Standby, and 0 indicates Single Station/Fault.

Does querying redundant OS servers directly degrade plant bus performance?

Yes, heavy SQL queries executed during shift changes can saturate OS server CPU and disk I/O, which is why Siemens recommends offloading long-term reporting to Process Historian.