Introduction

When I built my new desktop for Oracle RAC practice, I expected smooth sailing. Instead, I ran into persistent issues: high %irq, high %system CPU, and 100% disk utilization whenever I ran my RAC lab inside Oracle VirtualBox on Windows 11.

Even simple RAC test workloads caused the VM guests to lag. Tools like sar, mpstat, and iostat all pointed to interrupt storms (ksoftirqd) and high I/O wait. At first, I thought it was a VM misconfiguration—but the real problem was deeper: the Windows 11 host itself.

This article documents the troubleshooting steps, why the issue happened on Windows but not on macOS/Linux, and how switching my host OS to Linux completely resolved it.

Symptoms I Observed

• High %irq and %system in mpstat:

%usr  %sys  %iowait  %irq  %soft  %idle
0.7   1.0   44.2     6.3   1.1    46.8

• perf top showing:

47%  [kernel]  handle_softirqs
28%  [kernel]  pv_native_safe_halt
 7%  [kernel]  vbg_req_perform

• iostat reporting 100% utilization on VMs’ virtual disks, even with low throughput.
• On VMware too, the same pattern: high system usage, sluggish storage performance.

Root Causes

After weeks of debugging, I pinned down the main culprits:

1. Windows 11 Hyper-V / VBS / CrowdStrike filter drivers
   • Even with Hyper-V “disabled” in settings, Windows forces some virtualization layers (NEM).
   • Security filters (CrowdStrike network filter, Defender) also added overhead to VirtualBox/VMware networking and storage.
2. VirtualBox Bridged Networking on Windows
   • Bridged adapters created IRQ storms (NET_RX softirqs pegged CPUs).
   • Disabling the public NIC inside the VM dropped CPU usage instantly.
3. Storage Virtualization Overhead
   • Windows host caching, filters, and background indexing caused RAC’s heavy ASM/ACFS I/O to bottleneck.

On macOS/Linux, the same RAC lab with identical VM configs had none of these issues.

The Final Fix: Moving to Linux Host

I finally wiped Windows 11 and installed Oracle Linux 9 directly on my desktop. Immediately:

• %irq dropped to near zero.
• Disk I/O latency improved drastically (iostat shows <5ms).
• VMs felt snappy—no more stalls.

No special tuning needed beyond normal VM best practices.

Key Lessons Learned

1. Windows 11 is not ideal for Oracle RAC labs—its virtualization stack introduces overhead you can’t fully disable.
2. Linux is leaner for VM hosting—IRQ handling, disk I/O, and networking are far more efficient.
3. If you must use Windows, prefer:
   • NAT networking (not Bridged) with port forwarding.
   • Excluding VM folders from antivirus/security agents.
   • Using NVMe disks and fixed-size VM storage.
4. But the most reliable solution is: run your RAC labs on Linux host OS.