CKA Storage Practice Question
Which CSI driver feature must be supported by the driver to allow expanding a PVC while the pod using it is still running?
⚠ Common exam trap
Candidates may confuse the Kubernetes feature gate `ExpandInUsePersistentVolumes` with a CSI driver capability. The feature gate is a cluster-level setting, while the driver must support volume expansion via its CSI capabilities.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Volume expansion
To allow expanding a PVC while the pod is still running, the CSI driver must support volume expansion (e.g., ControllerExpandVolume and NodeExpandVolume RPCs). The in-use expansion capability is also controlled by the Kubernetes feature gate `ExpandInUsePersistentVolumes`, but that is not a CSI driver feature. Therefore, the correct answer is 'Volume expansion'.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Volume attach
Why it's wrong here
Volume attach refers to the CSI driver ability to attach a storage volume to a specific node through calls like ControllerPublishVolume. This is a prerequisite for using a volume but has no bearing on whether its capacity can be increased while a pod is using it. The question targets a capability specifically for online expansion, not attachment mechanics.
- ✓
Volume expansion
Why this is correct
Volume expansion is the correct high-level feature, but the CSIDriver spec requires an explicit mode to enable the in-use aspect. A driver may support expansion only when the volume is detached, declared via ExpandPersistentVolume, and still not allow resize while attached. Thus merely saying 'volume expansion' is too imprecise; Kubernetes must see a specific mode flag to permit online expansion.
- ✗
Mount options
Why it's wrong here
Mount options are string settings passed to the CSI driver during NodeStageVolume and NodePublishVolume for filesystem-specific behavior like read-only or mount propagation. They have no connection to the storage capacity or resizing logic of the underlying volume. Mount options govern how a volume is mounted on the node, not whether its size can be changed in place.
- ✗
ExpandInUsePersistentVolume
Why it's wrong here
ExpandInUsePersistentVolume is a value of the volumeExpansionModes field in the CSIDriver object, which explicitly advertises that the driver can expand a PersistentVolume while it is still attached and mounted to a running pod. When this capability is present, the kubelet can perform a filesystem resize after the controller-side volume expansion, without requiring pod or volume recreation. This is precisely the driver feature required to support online volume expansion.
Go deeper
Related to this question
Learn chapter
Kubernetes Architecture Overview
Key term
Network Policies
A Kubernetes resource that controls how pods communicate with each other and with other network endpoints, acting as a firewall for pod-to-pod traffic.
Key term
Ingress Resources
Ingress Resources are Kubernetes API objects that manage external access to services inside a cluster, typically HTTP and HTTPS traffic, by defining rules for routing requests based on hostnames and paths.
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