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Local PV LVM VAC Parameters

Overview​

VolumeAttributesClass (VAC) parameters allow you to define Quality of Service (QoS) policies for Local PV LVM volumes.

These parameters control IOPS and bandwidth limits for filesystem and block-mode volumes provisioned through Local PV LVM. QoS policies are enforced at the node level using Linux cgroup v2 controls.

Supported VAC Parameters​

The following VAC parameters are supported for Local PV LVM volumes.

ParameterDescriptionAccepted Values
qosIopsLimitMaximum Read/Write IOPS limitNon-zero positive integer or max
qosIopsReadLimitMaximum read IOPS limitNon-zero positive integer or max
qosIopsWriteLimitMaximum write IOPS limitNon-zero positive integer or max
qosBandwithPerSecMaximum Read/Write bandwidth per secondNon-zero positive integer (bytes/sec) or supported size suffixes such as 7000Mi
qosBandwithReadPerSecMaximum read bandwidth per secondNon-zero positive integer (bytes/sec) or supported size suffixes such as 7000Mi
qosBandwithWritePerSecMaximum write bandwidth per secondNon-zero positive integer (bytes/sec) or supported size suffixes such as 7000Mi
note

Setting an IOPS parameter to max disables IOPS limiting for that parameter on the volume. A value of 0 is not supported for IOPS or bandwidth parameters.

VAC parameter names are case-sensitive and must be written exactly as shown in the table above. A misspelled or differently cased name is rejected as an unsupported parameter rather than being ignored. Values must not have leading or trailing spaces.

Example VAC Configuration

The following example configures total IOPS and bandwidth limits using a VAC.

apiVersion: storage.k8s.io/v1
kind: VolumeAttributesClass
metadata:
  name: lvm-qos-high
driverName: local.csi.openebs.io
parameters:
  qosIopsLimit: "50000"
  qosBandwithPerSec: "5000000"

Example Directional QoS Configuration

The following example configures separate read and write QoS limits.

apiVersion: storage.k8s.io/v1
kind: VolumeAttributesClass
metadata:
  name: lvm-qos-directional
driverName: local.csi.openebs.io
parameters:
  qosIopsReadLimit: "100"
  qosIopsWriteLimit: "200"
  qosBandwithReadPerSec: "7000Mi"
  qosBandwithWritePerSec: "8000Mi"

Combining Unified and Directional Parameters​

qosIopsLimit and qosBandwithPerSec are unified parameters. Each one applies to both the read and the write direction, unless the matching directional parameter is also specified:

  • qosIopsLimit: "500" on its own limits both reads and writes to 500 IOPS.
  • qosIopsLimit: "500" together with qosIopsWriteLimit: "200" limits reads to 500 IOPS and writes to 200 IOPS.

The same applies to qosBandwithPerSec with qosBandwithReadPerSec and qosBandwithWritePerSec.

A unified parameter and a directional parameter of the same kind can be used together only when they do not contradict each other. If both are specified with different values, the VAC is rejected. Specifying the same value in both is accepted.

Update VAC QoS Parameters​

You can modify the QoS policy applied to a PVC by updating the volumeAttributesClassName field to reference a different VAC.

Example Updated VAC

apiVersion: storage.k8s.io/v1
kind: VolumeAttributesClass
metadata:
  name: lvm-qos-low
driverName: local.csi.openebs.io
parameters:
  qosIopsLimit: "20"
  qosBandwithPerSec: "20000"

Example Updated PVC

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: lvm-pvc
spec:
  accessModes:
    - ReadWriteOnce
  storageClassName: openebs-lvm
  volumeAttributesClassName: lvm-qos-low
  resources:
    requests:
      storage: 5Gi

Apply the updated PVC configuration:

kubectl apply -f pvc.yaml

After the PVC is updated, OpenEBS Local PV LVM automatically reconciles and applies the new QoS settings associated with the updated VolumeAttributesClass.

note

When a volume is moved to a different VAC, only the parameters present in the new VAC are applied. A parameter that the new VAC does not specify keeps the value that is already in effect on the volume and is not reset.

To remove a limit that was applied earlier, set that parameter to max in the new VAC instead of omitting it.

Invalid VAC Parameter Example​

Conflicting QoS Parameters

The following example uses conflicting QoS parameter values.

apiVersion: storage.k8s.io/v1
kind: VolumeAttributesClass
metadata:
  name: lvm-qos-conflict
driverName: local.csi.openebs.io
parameters:
  qosIopsLimit: "max"
  qosIopsReadLimit: "1000"

The unified parameter qosIopsLimit removes the IOPS limit for both directions, while qosIopsReadLimit sets a read limit of 1000 IOPS. As the two values contradict each other, the VAC is rejected and the QoS settings of the volume are left unchanged.

To apply these limits, use only the directional parameters:

apiVersion: storage.k8s.io/v1
kind: VolumeAttributesClass
metadata:
  name: lvm-qos-read-limited
driverName: local.csi.openebs.io
parameters:
  qosIopsReadLimit: "1000"
  qosIopsWriteLimit: "max"

Verify VAC QoS Configuration​

Use the following command to verify the PVC configuration.

kubectl describe pvc <pvc-name>

Expected Results

  • The PVC references the updated VAC
  • Updated QoS parameters are applied to the Local PV LVM volume
  • QoS reconciliation completes automatically on supported Kubernetes versions

Support​

If you encounter issues or have a question, file a Github issue, or talk to us on the #openebs channel on the Kubernetes Slack server.

See Also​