Resolving Tag Logging Archive Selection Failures on Redundant OS Standby Servers in PCS 7

In a SIMATIC PCS 7 redundant OS Server architecture (OS1 Master, OS2 Standby), an engineer cannot browse or select archive tags in WinCC Online Trend Control on the Standby Server (OS2) because redundant WinCC projects reference historical archives exclusively through the unified symbolic name of the redundant server pair (typically OS1 or the redundant package name). Because OS2 operates as a synchronized clone whose Tag Logging schema is mastered by OS1 on the ES, browsing local tags on OS2 fails or returns an empty selection window. To resolve this, always select the symbolic name of the redundant server pair as the data source in the Trend Control dialog, which grants transparent tag selection from any server or client workstation.

Redundant OS Server Archive Architecture and Symbolic Server Names

In SIMATIC PCS 7 (including V7.1, V8.2, and V9.0), high availability is achieved by deploying redundant OS Server pairs consisting of a Master server (OS1) and a Standby server (OS2). Both servers run independent Microsoft SQL Server database instances, independent Tag Logging engines (CCTlgServer.exe), and continuously synchronize process data, alarms, and trend archives across the Terminal Bus using the WinCC Redundancy Manager.

To present a unified interface to operator clients, WinCC abstracts the physical IPC hostnames into a single Symbolic Computer Name (or Server Package name), which by default inherits the name of the master station in SIMATIC Manager (e.g. OS1 or OS_SRV). When client workstations or local runtime controls query process archives, they query this symbolic entity, and the redundancy manager automatically routes the request to whichever physical server is currently active.

Why Local Archive Browsing Fails on the Standby Server (OS2)

Commissioning engineers frequently encounter an apparent anomaly when configuring trends locally on the Standby server (OS2):

Opening WinCC Online Trend Control on OS1 allows opening the tag selection dialog and browsing all Tag Logging Fast and Slow tags.
Opening the identical dialog on OS2 results in an empty tree, a blank tag list, or an error window.
Typing the tag name manually into the tag field using the format <ArchiveName>\<TagName> works normally and displays trends.
Opening the trend control on an Engineering Station or OS Client works normally even when OS2 is the active master.

The technical root cause: In SIMATIC Manager, the WinCC project is engineered solely on the master station (OS1) and copied to OS2 via Project Duplicator. On OS2, the local Tag Logging database editor operates in standby slave mode; its internal COM/OLE-DB browser does not resolve local physical tags under the computer name OS2. The browser only resolves tags when queried against the Symbolic Name of the Redundant Pair (OS1).

Comparison of Tag Selection Methods Across OS Redundancy Nodes

The following table compares the behavior of archive tag browsing across stations in a redundant PCS 7 architecture:

Station LocationData Source Selected in Trend ControlArchive Tag Browsing BehaviorTrend Display StatusMaster Server (OS1)Symbolic Server Name (OS1)100% Functional; full tree visibleActive and healthyMaster Server (OS1)Physical Hostname (OS1)FunctionalActive and healthyStandby Server (OS2)Physical Hostname (OS2)Fails; empty tag selection windowCannot bind tagStandby Server (OS2)Symbolic Server Name (OS1)100% Functional; full tree visibleActive and healthyStandby Server (OS2)Manual syntax: <Archive>\<Tag>Bypasses browser; binds directlyActive and healthyOS Client / ESSymbolic Server Name (OS1)100% Functional; full tree visibleTransparent failover across OS1/OS2

Step-by-Step Procedure to Configure and Select Redundant Archive Tags

Follow this procedure to ensure smooth archive tag selection and trend configuration across redundant servers:

Identify the Symbolic Server Name in SIMATIC Manager:
- In SIMATIC Manager Component View, look at the PC Station name representing the primary OS Server (e.g. OS(1) or OS1).
- In WinCC Explorer on OS1, open Server Data. The generated package name (e.g. OS1.pck) defines the symbolic name.
Configure WinCC Online Trend Control:
- In Graphics Designer, open the process mimic or trend screen.
- Double-click the WinCC Online Trend Control to open its configuration dialog.
- Navigate to the Trends tab.
- Under 'Data Source', select Archive Tags.
Select Tag via the Symbolic Server Package:
- Click the Select Tag button.
- In the selection tree on the left, do not select the local physical computer name (OS2).
- Select the Symbolic Server Name (e.g. OS1 or Project_OS).
- Expand the tree: TagLogging Fast and TagLogging Slow will populate with all configured archive tags.
- Select the desired process tag and click OK.
Deploy Screen to Redundant Stations:
- Save the picture in the ES master project.
- Use the WinCC Project Duplicator or SIMATIC Manager OS Download to transfer the project to OS1 and OS2.
- Open the trend screen on both OS1 and OS2; both will now display identical historical curves seamlessly.

Verification

Verify redundant trend operation in WinCC Runtime:
1. Open the trend window on OS1 and OS2 simultaneously. Confirm that historical data curves render identically on both screens.
2. Temporarily disconnect the network cable from OS1 to force redundancy failover to OS2.
3. Verify that the trend curves on OS2 and all OS Clients continue plotting live samples without interruption or flatlining.
4. Reconnect OS1, observe archive synchronization, and verify that no gaps appear in historical trend logs.

Limitations and Operational Precautions

Never Configure Independent Archive Tags on OS2: All Tag Logging configuration must occur on the Engineering Station inside the master OS project. Manually creating archive tags on the physical OS2 station corrupts redundancy database synchronization.
Redundancy License Requirement: Both servers must have active WinCC Redundancy licenses installed in Automation License Manager (6AV6371-1CA07-5AX0). Without redundancy licenses, archive synchronization between servers is disabled.
Server Package Regeneration: If new archive tags are added to Tag Logging, re-generate Server Data (Server Data -> Generate) on the ES and redownload to OS Clients to update client archive browsing directories.

Engineer FAQ

Why does typing the tag name manually work on OS2 while browsing fails?

Typing <ArchiveName>\<TagName> bypasses the graphical tag browser and directly binds the trend pen to the underlying WinCC OLE-DB database engine, which knows where to find the data. Browsing fails because the browser queries local computer objects rather than the symbolic server package.

Where do I find the symbolic server name?

In WinCC Explorer, expand 'Server Data'. The name of the generated .pck file (e.g. OS1.pck) is the symbolic server name representing the redundant server pair.

Does it matter which server is Master when viewing trends on OS Clients?

No. OS Clients communicate through the symbolic server package. If the Master fails, the WinCC Redundancy manager automatically switches client connections to the Standby server in under one second without disrupting historical trends.