Managing Disk Space and Multi-Drive Tag Logging Storage in SIMATIC Process Historian 2014

In SIMATIC Process Historian 2014, multi-drive extended storage configurations (such as Tag0 and Tag1) do not support automatic dynamic storage rebalancing when one partition exhausts capacity. Process Historian pre-allocates database filegroups according to rigid chronological or tag-type rules configured during commissioning. Resolving storage exhaustion on a single tag drive requires applying PH 2014 SP3 Update 2 or later, implementing automated detachment and offloading of older segment files (*.bck) to secondary NAS/SAN storage, or executing SQL Server database file relocation procedures.

Storage Architecture and Partitioning in Process Historian 2014

SIMATIC Process Historian (PH) 2014 SP3 operating in an extended hardware configuration (such as enterprise HPE ProLiant Gen10 servers with integrated SAN and external NAS) partitions SQL Server data across multiple dedicated physical drive arrays:
* Operating System & Application: Drive C:
* Database System Catalog (MDF/LDF): High-speed RAID volume (e.g., Drive D:)
* Alarm Archives: Dedicated alarm database volume
* Tag Logging Archives (Tag0, Tag1, etc.): Partitioned across separate volumes to balance disk I/O throughput across independent RAID controllers or SAN LUNs.

The Storage Balancing Dilemma

In high-volume installations (e.g., logging 8,000+ continuous analog tags):
1. Static Filegroup Allocation: Process Historian does not provide a dynamic, real-time "storage balancer" that reroutes incoming data to Tag0 when Tag1 approaches full capacity. The underlying Microsoft SQL Server database partitions segment files into specific filegroups based on predefined project configuration schemas.
2. Segment Growth Discrepancies: If fast-acquisition tags or high-frequency analog signals are mapped to filegroups hosted on Tag1, that volume fills significantly faster than Tag0.
3. Known Internal Project Structure Defect: Early releases of PH 2014 SP3 contained an internal storage allocation defect where temporary tables and growing database segments accumulated disproportionately. Siemens addressed this in PH 2014 SP3 Update 2 under the title Storage Space Optimization of Internal Project Structure.

Step-by-Step Procedure to Resolve Storage Exhaustion

Follow this procedure to recover disk capacity on the exhausted tag volume and establish sustainable long-term archiving.

Prerequisites

Windows Administrative credentials on the Process Historian server.
Confirmed availability of external secondary storage (e.g., dedicated NAS share or SAN volume).
Verified recent database backup.

Step 1: Verify and Apply Process Historian Updates

Open the Windows Control Panel -> Programs and Features -> Installed Updates.
Check the installed version of Process Historian.
If running base PH 2014 SP3, apply PH 2014 SP3 Update 5 (or the latest cumulative update). This ensures all storage optimization patches, segment cleanup fixes, and database maintenance scripts are active.

Step 2: Configure Automated Segment Backup and Detachment to NAS

Launch the Process Historian Management Console.
Navigate to Backup & Restore -> Automatic Backup.
Enable automated backup and set the destination path to your network-attached storage:
\\NAS_Storage\PH_Archives\Segments
Set the Detachment Policy:
* Configure older passive segments (e.g., segments older than 30 or 60 days) to detach automatically once the .bck file is verified on the NAS.
* Enable the option to Delete detached database files from local disk after successful archive confirmation.
This immediately frees hundreds of gigabytes on local Tag volumes while preserving long-term query capabilities via offline segment mounting.

Step 3: Execute Manual Segment Detachment

In the Process Historian Management Console, navigate to Database Management -> Archive Segments.
Filter segments hosted on drive Tag1.
Identify the oldest completed weekly/monthly passive segments.
Right-click each completed segment, select Backup Segment, and once backed up, select Detach Segment.
Confirm that the corresponding .mdf and .ldf files are removed from Tag1, restoring free storage space.

Step 4: Relocate SQL Database Secondary Files (Advanced Maintenance)

If immediate relief is required without detaching segments:
1. Schedule a maintenance window and stop the Process Historian services via the Management Console.
2. Open Microsoft SQL Server Management Studio (SSMS) with administrative credentials.
3. Detach the specific passive segment or secondary database partition.
4. Move the physical database files (.ndf) from the congested drive Tag1 to the underutilized drive Tag0.
5. Re-attach the database pointing to the new physical file path on Tag0 using ALTER DATABASE [DB_Name] MODIFY FILE (NAME = ..., FILENAME = 'Tag0_Path\...').
6. Restart Process Historian services and verify catalog synchronization.

Verification

In Windows File Explorer, monitor drive Tag1: confirm that free disk space increases substantially (e.g., maintaining a minimum of 20% to 30% free capacity).
In Process Historian Management Console, verify that active writing segments continue to log incoming process tags without status warnings.
Run a sample report in WinCC Information Server across both recent and detached historical periods to ensure continuous data retrieval.
Check Windows Event Viewer under Applications and Services Logs -> Siemens -> Process Historian to confirm zero disk full or write-lock events.

Limitations and Operational Precautions

Never Delete Database Files Manually in Windows Explorer: Deleting .mdf, .ldf, or .ndf files from Windows Explorer corrupts the SQL instance and irreversibly damages historical data. Always use the PH Management Console to detach segments.
Minimum Free Space Threshold: Process Historian halts active runtime archiving if free disk space on any active database drive falls below a critical threshold (typically 5 GB to 10 GB), triggering emergency data buffering on OS Servers.
NAS Network Bandwidth: Ensure the network connection between the Process Historian server and the NAS has dedicated gigabit throughput to prevent backup timeouts during segment transfers.

Engineer FAQ

Can Process Historian automatically balance data between Tag0 and Tag1?
No. PH 2014 does not feature dynamic automatic storage rebalancing between active tag drives. Data allocation is fixed by filegroup assignment during commissioning.
What happens if a tag logging drive fills up completely?
If a drive reaches 100% capacity, Microsoft SQL Server suspends write transactions. Process Historian stops accepting tags from OS Servers, causing OS Server SFCache buffers to fill and eventually leading to data loss.
What did PH 2014 SP3 Update 2 fix regarding storage?
Update 2 corrected an issue where internal project structures and temporary segment tables failed to release disk space after segment closure, leading to artificial drive congestion.
Can detached segments be viewed again in WinCC Information Server?
Yes. Using the PH Management Console, any detached .bck segment on the NAS can be restored and mounted online within minutes for auditing or reporting.
Can I resize or combine Tag0 and Tag1 into a single volume?
Yes. In virtualized SAN environments, modern practice favors configuring a single large, high-performance RAID/SAN volume for all tag data rather than splitting into multiple smaller fixed drives.

Technical References

Siemens Industry Online Support Entry ID 66579062: Process Historian Administration and Maintenance Manual.
Siemens Industry Online Support Entry ID 109755371: Siemens Technical Support Expert Consultation for Process Historian.
Microsoft SQL Server Technical Documentation: Managing Database Filegroups and File Relocation.

Managing Disk Space and Multi-Drive Tag Logging Storage in SIMATIC Process Historian 2014