The Splunk Enterprise Capacity Planning Manual states that running Splunk in a virtualized environment typically results in a performance reduction of approximately 20% to 45% compared to equivalent deployments on physical hardware.

This degradation is primarily due to the virtualization overhead inherent in hypervisor environments (such as VMware, Hyper-V, or KVM), which can affect:

Disk I/O throughput and latency — the most critical factor for indexers.

CPU scheduling efficiency, particularly for multi-threaded indexing processes.

Network latency between clustered components.

Splunk’s documentation strongly emphasizes that while virtualized environments offer operational flexibility, they cannot match bare-metal performance, especially under heavy indexing loads.

To mitigate performance loss, Splunk recommends:

Reserving dedicated CPU and I/O resources for Splunk VMs.

Avoiding over-commitment of hardware resources.

Using high-performance SSD storage or paravirtualized disk controllers.

These optimizations can narrow the performance gap, but a 20–45% reduction remains a realistic expectation under typical conditions.

References (Splunk Enterprise Documentation):

• Splunk Enterprise Capacity Planning Manual – Virtualization Performance Considerations

• Splunk on Virtual Infrastructure – Best Practices and Performance Tuning

• Indexer and Search Head Hardware Recommendations

• Performance Testing Guidelines for Splunk Deployments