VMware ESXi High Disk Latency – Practical Troubleshooting

High storage latency is one of the most common causes of VM performance degradation. This runbook focuses on fast, non-disruptive diagnostics before any invasive changes are made.

Symptoms

• Slow VM response or freezes

• vSphere alerts for datastore latency

• High DAVG or KAVG values

• IO wait inside guest operating systems

Environment

• VMware ESXi 7.x / 8.x

• VMFS or NFS datastores

• Block or NAS-based storage

Common Root Causes

• Storage contention

• Path failures or degraded multipathing

• Snapshot accumulation

• Queue depth saturation

• Misaligned backup or replication jobs

Fix Path (SAFE – Read-Only Diagnostics)

Step 1: Identify Affected Datastores

Step 2: Check Device Latency

Press:

• u → disk device view

Key metrics:

• DAVG > 20ms = storage issue

• KAVG > 2ms = host/kernel issue

Step 3: Verify Path Health

Look for:

Step 4: Snapshot Inspection

Verification

• Observe latency trends in esxtop

• Confirm VM responsiveness improves

• Validate no paths are in dead/standby unexpectedly

Rollback

This runbook does not modify configuration.
If changes were made later (queue depth, storage policies), revert to vendor defaults.