Diagnosing Process Historian 'Tag Recovery Needed' and Missing Tag Archives After WinCC Redundancy Duplication

In SIMATIC PCS 7 and WinCC SCADA architectures interfaced with SIMATIC Process Historian (PH), the condition where Process Historian receives alarm events normally but shows 'Tag Recovery Needed' and logs zero process values typically occurs when a WinCC project is modified on the Engineering Station and transferred to redundant OS Servers using the WinCC Project Duplicator incorrectly. This action resets or desynchronizes the internal Tag Logging archive GUIDs and Redundancy state machines. To resolve this, engineers must verify that the PH Ready component versions match across all OS servers and the PH, re-establish WinCC Redundancy synchronization, ensure the WinCC Project Duplicator is never used on live active server pairs without stopping clients, and perform a manual archive synchronization via the Process Historian Management Console.

Process Historian Architecture and Data Ingestion Pipeline

The SIMATIC Process Historian (PH) serves as the central long-term archiving database for SIMATIC PCS 7 and WinCC. It interfaces with OS Servers via the Process Historian Ready Component (PH-Ready) service installed on every WinCC server station. The data ingestion pipeline operates via two independent streaming channels:

Message / Alarm Stream: WinCC Alarm Logging pushes discrete sequence-of-events records to the PH message buffer via SQL service-broker queues.
Process Value / Tag Logging Stream: Fast and Slow Tag Logging segments store high-speed compressed floating-point archives in local Microsoft SQL Server segments (.mdf/.ldf), which are then transferred in chunks to the PH database.

Because alarm data and tag data utilize separate queuing mechanisms, a breakdown in archive GUID alignment or database synchronization will halt tag archiving while leaving alarm logging completely functional.

Root Cause Analysis: Why Duplication Breaks Tag Archiving

The scenario described by users—modifying a WinCC project on an ES and duplicating it onto live redundant servers (OS_Master and OS_Standby) using the WinCC Project Duplicator—is a critical procedural mistake:

Archive GUID Desynchronization: When Project Duplicator performs a 'Save As' or duplicate operation, it generates a fresh, unique database identifier (GUID) for the local WinCC archive segment. The Process Historian, however, tracks the existing server pairing using the old GUID. Finding mismatched archive identities, PH flags the data source as invalid and halts automated tag ingestion.
'Tag Recovery Needed' Status: In the Process Historian Management Console (PHMC) under 'Data Sources', the status Needed indicates that PH has detected an unbridgeable time gap or GUID discontinuity between the server's local archive segments and the PH database.
Deactivation While Clients Connected: Modifying project files and duplicating while clients remain connected leads to locked SQL transaction logs (.ldf), causing orphaned tag references.

PH-Ready Component Version Matching and Diagnostic Checks

A frequent technical prerequisite often overlooked during updates is exact component parity:

PH-Ready Component Version: The version of the PH-Ready service installed on the WinCC OS Servers must match the exact service pack and update level of the Process Historian server (e.g., PH 2014 SP2 requires PH-Ready 2014 SP2 on all OS servers).
Check PH Diagnostic Logs: On the OS Server, navigate to C:\Program Files (x86)\Siemens\Process Historian\Diagnostics. Inspect PHReadyComponent.log and ArchiveManager.log for SQL authentication errors or 'Archive GUID rejected' entries.
Verify Message Queuing (MSMQ): Ensure the Windows Message Queuing service is running and that private queues (ph_tag_queue, ph_alarm_queue) are not clogged or showing quota overruns.

Correct Procedure for Project Transfer to Redundant OS Servers

In standard PCS 7 engineering, the WinCC Project Duplicator should NEVER be used to manually copy files between ES and OS. The proper procedure is:

Standard Download from SIMATIC Manager: In SIMATIC Manager, right-click the target OS object and choose PLC > Download. This utilizes the native PCS 7 OS Loader, which automatically manages server switchover, updates runtime databases bumplessly, and preserves archive GUIDs.
If Project Duplicator MUST Be Used (Standalone WinCC):
a. Stop WinCC Runtime on the Standby Server (SERV_B).
b. Use Project Duplicator to duplicate from ES to SERV_B.
c. Start SERV_B; wait until redundancy synchronization completes (all clients connected to SERV_B).
d. Stop WinCC Runtime on Master Server (SERV_A).
e. Use Project Duplicator (Duplicate Redundant Partner) to synchronize SERV_B back to SERV_A.
Trigger Manual Tag Recovery in PHMC: In PHMC, navigate to Data Sources > Select OS Server, right-click and select Start Tag Recovery. Specify the start and end timestamp of the missing period to force PH to pull the missing segments from the WinCC server.

Comparison of Online Project Transfer Methods in WinCC

The following table compares the risks and operational impact of different project deployment methods to redundant WinCC / PCS 7 servers:

Deployment MethodArchive GUID ContinuityProcess Historian ImpactRedundancy HealthRecommended DeploymentSIMATIC Manager 'PLC > Download'Preserved bumplesslySeamless continuous archivingAutomatic switchover handledMandatory for all PCS 7 systemsManual Project Duplicator (Improper)Broken (Generates new GUID)'Tag Recovery Needed' / Lost TagsHigh risk of split-brain statusStrictly discouraged in PCS 7Proper Duplication Sequence (Offline)Preserved if duplicated partner-to-partnerRequires manual tag recovery triggerSynchronized after dual rebootPermitted only in standalone WinCCDirect Windows File Copy in ExplorerCorrupted SQL databasesComplete failure of all archivingSevere SQL database corruptionProhibited under all circumstances

Verification

Verify that Process Historian tag ingestion has been successfully restored:
1. Open the Process Historian Management Console (PHMC) on the PH Server.
2. Navigate to Data Sources; verify that the connection status to both SERV_A and SERV_B displays 'Connected / Active' with a green checkmark.
3. Confirm that the 'Tag Recovery' state changes from Needed to Idle / Finished.
4. Launch the Process Historian Dashboard or SIMATIC Information Server; generate a trend report for an active analog tag (e.g., TIC_201.PV_Out#Value) and verify that continuous historical curves display without gaps.

Limitations and Operational Precautions

Never perform manual file operations, backups, or deletions directly inside the WinCC SQL archive folders (ArchiveManager\TagLoggingFast or TagLoggingSlow). These folders are dynamically locked by SQL Server and the WinCC DataManager. Triggering a large Process Historian tag recovery across multiple months of data can place substantial I/O load on the OS server storage subsystem; schedule manual recoveries during off-peak operational hours.

Engineer FAQ

Why did Process Historian continue receiving alarms even when tags were not stored?

Alarms and process tags use completely different logging mechanisms. Alarms are pushed as event messages via the SQL broker/MSMQ queue, whereas Tag Logging relies on local file segment archiving and GUID matching before bulk streaming to PH.

What does 'Tag Recovery Needed' mean in the PH Management Console?

It indicates that Process Historian detected a time discontinuity or archive segment gap between its database and the WinCC OS Server, requiring an archive recovery to retrieve the missing historical data.

Can I run different versions of PH-Ready on the OS Servers than the Process Historian version?

No. The PH-Ready communication service is tightly coupled to the internal database schema and communication protocols of the Process Historian. Running mismatched versions will cause silent connection drops and archiving failures.