PCS7 Long-Term Archiving: StoragePlus vs CAS vs Process Historian

Overview: PCS7 Long-Term Archiving Options

Siemens SIMATIC PCS 7 provides three distinct mechanisms for moving process values, messages, and audit-trail data out of the live WinCC Runtime databases and onto durable, queryable media. They are not interchangeable:

• StoragePlus — bundled viewer and offline archive management add-on for the OS server or a standalone station.
• CAS (Central Archive Server) — a dedicated redundant pair that aggregates archives from one or more OS servers and serves a seamless online/offline view to every client on the plant network.
• Process Historian (PH) — the strategic, SQL-based replacement for CAS introduced with PCS 7 V8.0. Adds high-performance bulk query, data-mining APIs, and native Microsoft Reporting Services integration.

All three sit behind the WinCC/PCS 7 OS server — they do not replace the standard cyclic and acyclic archives that the OS server maintains in memory and on local disk. They consume segments that the OS server flushes from its Tag Logging / Alarm Logging runtime databases, so they inherit the same tag model, time stamping, and compression behavior configured in the OS project.

StoragePlus — Technical Details

StoragePlus (Siemens article ID 6ES7658-1.../2..., WinCC option V6.0+) is the smallest of the three options. It consists of two components:

1. StoragePlus Server service running on the OS server (or on a dedicated station) that exports completed WinCC segments to removable or networked storage.
2. StoragePlus Viewer — an add-in to WinCC Explorer / WinCC Runtime that lets an operator transparently query both the online segment buffer and the exported (offline) segments.

Export targets supported:

• Tape (LTO via Windows Removable Storage Service — requires a 3rd-party RSM provider)
• DVD / Blu-ray (via Windows IMAPI)
• Network shares (SMB / CIFS)
• External USB / RDX cartridges

What StoragePlus does NOT do:

• No aggregation of multiple OS servers.
• No SQL interface — data is read via the proprietary StoragePlus viewer only.
• No native report generation beyond standard WinCC report designer output.
• No redundant pair — single-instance service.

Typical sizing: One StoragePlus instance per OS server. Disk footprint equals sum of all segments exported plus ~5 % index overhead. Export cadence is configurable per segment (commonly daily or weekly). Segments are typically 500 MB to 2 GB each; smaller segments reduce data-loss exposure on crash but increase index size.

Central Archive Server (CAS) — Technical Details

CAS is the historical workhorse for PCS 7 V6 through V7.1. It is built from two Windows services that must be installed on a separate, dedicated server pair:

Redundancy: CAS is licensed and deployed as a redundant pair (master + standby). The standby uses a Microsoft SQL Server log-shipping style mechanism; failover is automatic but not seamless for active client queries — clients must reconnect.

Reporting: CAS exposes a proprietary, C/C++ based API (the "CAS-ODK") and a COM interface. There is no native ODBC/SQL view of process data. Reporting is performed through:

• Crystal Reports via the CAS-ODK bridge (legacy, but commonly deployed).
• Custom C#/.NET applications using the CAS-COM wrapper.
• CSV export of selected tag ranges.

Limits to consider: CAS performance degrades noticeably above ~50,000 archived tags per server and ~5 years of online retention. The proprietary file format also makes forensic / regulatory exports (FDA 21 CFR Part 11, EMA Annex 11) more onerous than the SQL-backed PH.

Process Historian (PH) — Technical Details

SIMATIC Process Historian was introduced in PCS 7 V8.0 as the strategic replacement for CAS. Available under the catalog number 6ES7652-1... (PH Server) and 6ES7652-1...-... (PH Redundancy option), it ships with the following components:

• PH Server service (PHServer.exe) backed by Microsoft SQL Server 2008 R2 / 2012 / 2014 / 2016 / 2019 (depending on PH version) using a tuned schema optimized for time-series insertion.
• PH Connector on each OS server — replaces the older CAS Connector and pushes completed segments to PH in compressed batches.
• PH OPC UA Server — exposes historical data over OPC UA HDA (Historical Access) so third-party dashboards, Energy Manager PRO, and MindSphere can consume it.
• PH Information Server (separate license, optional) — web-based reporting portal built on Microsoft Reporting Services (SSRS).

Hardware baseline (PH Server, V9.0/V9.1):

Performance envelope: With appropriate sizing the PH is rated for >500,000 process values/s ingestion and queries returning 30-day aggregates across 1 million tags in under 5 s — roughly an order of magnitude over CAS. The PH also supports tag compression on insert (swung-gate / minmax), which CAS does not.

Reporting integration: Because PH data lives in SQL Server, any tool that can talk ODBC/JDBC/OLE DB can read it — without a proprietary bridge:

• Microsoft SSRS via the bundled Information Server add-on.
• Power BI (DirectQuery against the PH SQL schema).
• SAP BW/4HANA via the BAPI / RFC connector.
• Simatic IT Historian (for MES/ERP integration — significantly more costly).

Feature Comparison

Architectural Topology

The three options are not strictly mutually exclusive at the OS-server level, but in practice you deploy exactly one. The diagram below shows the recommended placement relative to a redundant OS server pair.

Selection Criteria

Use the matrix below as a field-proven decision shortcut:

Licensing and Version Compatibility

License keys are delivered as .zip Wibu-Sentinel containers and activated via the Automation License Manager (ALM). Counted licenses: each OS server needs one Connector license; the PH/CAS server itself needs one Server license; reporting clients need Information Server named-user or concurrent licenses.

Commissioning — Process Historian Quick Procedure

1. Install Windows Server 2019 on a dedicated VM or physical machine. Join the same domain as the OS servers.
2. Install Microsoft SQL Server 2019 Standard (or Enterprise for > 128 GB RAM). Set the SQL service account to a domain user with "Log on as service" rights.
3. Mount the SIMATIC PCS 7 V9.1 installation medium, run SIMATIC PCS 7 Setup → Process Historian. Choose single server or redundant pair.
4. After install, start the PH Configuration Console. The wizard creates the PH database (PHDB) on the local SQL instance, sets recovery model to SIMPLE, and configures file growth at 1 GB increments on a dedicated LUN.
5. On each OS server, install the PH Connector package. In WinCC Explorer, open Computer → Properties → Process Historian and enter the PH server name(s) plus the SQL login configured in step 4.
6. In the OS project, open Tag Logging → Archives → Properties → Process Historian. Enable Forward to PH per archive. Default transfer trigger: 50 % segment fill or 24 h, whichever comes first.
7. Rebuild the OS server; restart the CCArchiveServer (replaced by PHConnector) and the PHServer services.
8. Validate ingestion with the SQL query:

   SELECT TOP 50 [TagName], [Timestamp], [Value], [Quality]
   FROM PHDB.dbo.Archive
   WHERE [TagName] LIKE '%FLOW%'
   ORDER BY [Timestamp] DESC;

9. Install Information Server on a separate web front-end (or co-located), point it to the PH SQL instance, and publish the first SSRS report from the template library.

Commissioning — StoragePlus Quick Procedure

1. On the OS server, run SIMATIC Setup → Options → StoragePlus.
2. Launch StoragePlus Configurator from WinCC Explorer. Define at least one target (e.g., \\BACKUP01\Historian$) and one schedule (e.g., daily 02:00, retain 30 days online).
3. Map each archive to the target. Set minimum segment age to 24 h to avoid exporting an active segment.
4. Install the StoragePlus Viewer on every client that needs historical access. The viewer transparently merges online and offline data.
5. Test restore: pick an exported segment in the viewer, export to CSV, validate against the live archive for a known time window.

Verification Checks

Troubleshooting Matrix

Field-Proven Caveats

• Tag count ≠ throughput. PH performance is dominated by the number of changes per second, not the number of configured tags. A 100 k tag plant with 1 k changing tags is trivial; a 10 k tag plant with 90 k changing tags is hard.
• Anti-virus exclusions: Always exclude the PH data directory, the SQL .mdf/.ldf paths, and the WinCC project paths from real-time AV scanning. Microsoft SQL Server and the PH services have known issues when AV intercepts segment writes.
• Time sync: All OS servers, the PH server, and any Information Server must be on the same NTP source with < 100 ms skew. PH uses the SQL server time for the InsertTime column, not the source OS server time.
• Backup interaction: A PH database that is part of a SQL AlwaysOn AG cannot use the standard PH backup routine — coordinate with the DBA team and use COPY_ONLY backups or secondary replica snapshots.
• Memory-mapped WinCC segments: Never copy or move a still-open *.ldf segment file in Tag Logging. StoragePlus correctly waits for segment close, but manual file copies can corrupt the segment index.

Related Documentation

• SIMATIC PCS 7 Process Historian (PH) V9.1 manual
• SIMATIC PCS 7 Process Historian Information Server V9.1 manual
• WinCC/StoragePlus configuration manual
• SIMATIC PCS 7 V8.0 — What's new in Process Historian
• SIMATIC PCS 7 V9.1 system documentation