Stabilizing Virtualized SIMATIC PCS 7 v8.2 on VMware ESXi 6.5 - Resolving WinCC Explorer Freezes and OS Download Failures

In virtualized SIMATIC PCS 7 v8.2 environments hosted on VMware ESXi 6.5, symptoms including WinCC Explorer freezing indefinitely during project close, 'Out of Memory' crashes when launching Graphics Designer, failed OS downloads requiring manual 'Reset_WinCC' scripts, and multi-hour client startup synchronization delays are caused by memory overcommitment, non-reserved vCPU configurations, and misconfigured virtual network switches. PCS 7 requires strict 100% memory reservation (zero ballooning), dedicated vCPU pinning, VMXNET3 virtual network adapters with Promiscuous Mode enabled on the Terminal Bus vSwitch, and proper Windows desktop heap allocations.

Hardware Virtualization Pitfalls in SIMATIC PCS 7

Deploying SIMATIC PCS 7 v8.2 within a virtualized infrastructure (e.g. VMware vSphere / ESXi 6.5 on enterprise Dell PowerEdge R630 servers) offers significant advantages in hardware consolidation and disaster recovery. However, standard IT virtualization policies that rely on dynamic resource sharing are catastrophic for real-time industrial automation:
- The Pitfall of Resource Overcommitment:
* In commercial IT, hypervisors dynamically reclaim memory using memory ballooning (vmmemctl) and share CPU cycles across bursty workloads.
* In PCS 7, Microsoft SQL Server (WINCC), Alarm Logging (CCAlgRtServer.exe), and Tag Logging continuously maintain active in-memory caches. If ESXi attempts to balloon or swap WinCC RAM to physical SSD disk, SQL transactions stall, triggering cascading application deadlocks and 'Not Responding' states.
- The 'Out of Memory' Paradox:
* An ES or OS virtual machine configured with 8 GB of RAM can display 'Out of Memory' when opening Graphics Designer if the Windows Desktop Heap is exhausted, or if hypervisor memory throttling prevents WinCC GDI resource allocation.

Memory and CPU Resource Reservation in VMware ESXi

To guarantee deterministic real-time performance on VMware ESXi:

Enforce 100% Memory Reservation:
- In VMware vSphere Client, power down the target VM (e.g. OS_Server1).
- Edit VM Settings > Virtual Hardware > Memory.
- Check the box: Reserve all guest memory (All locked).
- This ensures that 100% of the allocated RAM (e.g. 8192 MB) is dedicated exclusively to the VM, completely disabling ESXi memory ballooning, hypervisor page sharing, and swapping.
CPU Core Sizing and Sockets:
- Allocate 4 vCPUs configured as 1 socket with 4 cores (or 2 sockets with 2 cores).
- Under CPU > Reservation, set a guaranteed CPU reservation (e.g. minimum 8000 MHz).
- Set Shares to High to ensure automation processes take precedence over non-critical VMs.

Terminal Bus Virtual Switch Configuration and Simatic Shell Broadcasts

Multi-hour client synchronization delays and clients failing to locate servers upon startup are directly tied to virtual network adapter and vSwitch settings:

Deploy VMXNET3 Adapters:
- Never use legacy E1000 or E1000E virtual network cards for PCS 7 stations. E1000 emulation introduces severe CPU interrupts and dropped UDP broadcast frames.
- Configure all PCS 7 VMs with VMXNET3 virtual network adapters.
Virtual Switch Security and Multicast Settings:
- In ESXi Networking, select the vSwitch or Port Group hosting the Terminal Bus.
- Under Security:
- Set Promiscuous Mode to Accept.
- Set MAC Address Changes to Accept.
- Set Forged Transmits to Accept.
- Simatic Shell relies on Layer-2 broadcast and multicast discovery frames. Standard ESXi security blocks these frames by default, preventing OS Clients from discovering the OS Server project until slow unicast polling succeeds hours later.

Redundancy Synchronization Optimization and Windows Desktop Heap

Resolving desktop crashes and download lockups:

Expanding Windows Desktop Heap:
- On the Engineering Station and OS Servers running Windows 7 / Windows Server 2012 R2:
- Open Windows Registry (regedit) and navigate to:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\SubSystems
- Open the string value Windows.
- Locate the parameter: SharedSection=1024,20480,768.
- Increase the interactive and non-interactive desktop heap allocations to:
SharedSection=1024,20480,2048 (or SharedSection=1024,30720,4096).
- This permanently eliminates 'Out of Memory' errors when launching Graphics Designer alongside SIMATIC Manager.
Resolving Download Lockups:
- When downloading an OS project from ES to OS Server, the ES initiates a remote project deactivation.
- Ensure the user account on ES and OS has identical administrative credentials across the workgroup or domain.
- Add both station IP addresses and hostnames into the Windows hosts file (C:\Windows\System32\drivers\etc\hosts) to eliminate NetBIOS resolution timeouts during project shutdown.

VMware ESXi VM Sizing and Resource Parameter Table

The following table details certified virtualization settings for SIMATIC PCS 7 v8.2:

Virtual Machine RoleRecommended vCPUsGuaranteed CPU ReservationAllocated RAMMemory ReservationVirtual NIC TypeEngineering Station (ES)4 vCPUs8,000 MHz8 GB to 16 GB100% LockedVMXNET3 (Dual NIC)OS Server (Redundant)4 vCPUs8,000 MHz8 GB to 12 GB100% LockedVMXNET3 (Plant + Terminal)OS Client (Operator)2 vCPUs3,000 MHz4 GB100% LockedVMXNET3 (Terminal Bus)Process Historian (PH)8 vCPUs16,000 MHz16 GB to 32 GB100% LockedVMXNET3 (Dual Gigabit)

Verification

To confirm that the virtualized PCS 7 environment has achieved complete operational stability:
1. In ESXi vSphere Client, select the OS Server VM and verify under Resource Allocation that Memory Overcommit displays 0 MB and Memory Reservation shows 8192 MB (100%).
2. Open SIMATIC Manager and launch Graphics Designer. Confirm that Graphics Designer opens in less than 3 seconds without 'Out of Memory' dialogs.
3. Perform an OS project download from the ES to the Standby OS Server. Verify that project closing, file transfer, and project reopening execute smoothly without freezing.
4. Reboot an OS Client VM:
- Confirm that the client boots into Windows.
- Verify that Simatic Shell discovers the active OS Server immediately.
- Confirm that the client launches WinCC Runtime and displays live process data in under 2 minutes rather than several hours.

Limitations and Operational Precautions

When managing virtualized PCS 7 environments:
1. Never Take VMware Snapshots While Runtime Is Active: Taking or reverting hypervisor snapshots while WinCC is actively archiving corrupts Microsoft SQL Server database page sequences. Always stop WinCC Runtime before taking VM snapshots.
2. Never Enable VMware vMotion for Active OS Servers: Live migrating (vMotion) an active WinCC OS Server while it is communicating with S7-400 controllers can introduce a momentary network pause (> 500 ms) that trips S7 fault-tolerant connection watchdogs, triggering false server redundancy switchovers.
3. Synchronize VM Time to ESXi Host with NTP: Disable VMware Tools periodic time synchronization in VM settings (tools.syncTime = "FALSE") and synchronize all VMs strictly via external NTP (SICLOCK) to prevent time jumps.

Engineer FAQ

Why does Graphics Designer report 'Out of Memory' when the VM has 8 GB of free RAM?

Graphics Designer utilizes the Windows GDI/USER Desktop Heap, which is limited by default to a small pool (typically 20 MB) regardless of total physical RAM. Expanding the SharedSection registry parameter resolves this bottleneck.

Can I use standard VMware vSwitch or do I need Distributed Virtual Switch (vDS)?

Standard vSwitches are fully certified and sufficient for PCS 7, provided Promiscuous Mode and MAC address spoofing are enabled on the Terminal Bus port group.

Why did OS downloads get stuck at 'Closing Project' on the server?

This occurs when WinCC runtime child processes (like CCAlgRtServer.exe) fail to detach their SQL Server locks within the timeout window due to hypervisor CPU throttling or DCOM permission stalls.