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BlockChaos allows you to inject delays into I/O operations on block devices and persistent volumes, simulating slow disk performance.

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Actions

BlockChaos currently supports:
  • delay: Add latency to I/O requests on block devices

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Spec Fields

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spec.action
string
required
The block chaos action to perform.Options: delay
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spec.volumeName
string
required
Name of the persistent volume to target.
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spec.delay
object
Delay configuration for I/O operations.
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spec.duration
string
Duration of the chaos action (e.g., 30s, 5m, 1h).
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spec.selector
object
required
Pod selector to target specific pods. See Selector for details.
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spec.mode
string
required
Selection mode for target pods.Options: one, all, fixed, fixed-percent, random-max-percent
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spec.containerNames
array
List of container names to affect. If not set, the first container will be injected.
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spec.remoteCluster
string
Remote cluster name where the chaos will be deployed.

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Examples

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Add I/O Delay to Persistent Volume

apiVersion: chaos-mesh.org/v1alpha1
kind: BlockChaos
metadata:
  name: hostpath-example-delay
spec:
  selector:
    labelSelectors:
      app: hostpath-example
  mode: all
  volumeName: hostpath-example
  action: delay
  delay:
    latency: 1s
This example adds 1 second of latency to all I/O operations on the hostpath-example volume for pods with the label app: hostpath-example.

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Add I/O Delay with Jitter

apiVersion: chaos-mesh.org/v1alpha1
kind: BlockChaos
metadata:
  name: disk-delay-jitter
spec:
  selector:
    namespaces:
      - database
    labelSelectors:
      app: postgres
  mode: all
  volumeName: postgres-data
  action: delay
  delay:
    latency: 100ms
    jitter: 50ms
    correlation: "50"
  duration: "5m"
This example adds 100ms base latency with 50ms jitter (50-150ms range) and 50% correlation between consecutive delays to simulate realistic disk variability.

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Prerequisites

  1. Persistent Volume: The target volume must be mounted in the pod
  2. Volume Name: You must know the name of the persistent volume (not the PVC name)
  3. Privileged Access: Chaos Daemon needs privileged access to manipulate block devices

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Implementation Details

BlockChaos works by:
  1. Identifying the block device associated with the specified volume
  2. Using eBPF or kernel modules to intercept I/O operations
  3. Adding configured delays to I/O requests
The delay parameters allow you to simulate:
  • Constant delay: Set latency only
  • Variable delay: Add jitter for randomness
  • Correlated delay: Use correlation to make consecutive delays similar (simulating sustained disk slowness)
Source: api/v1alpha1/blockchaos_types.go:35-73

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Limitations

  • Currently only supports the delay action
  • Requires knowledge of the persistent volume name (check with kubectl get pv)
  • Cannot target specific files or directories within a volume

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