Using top block-io
The top block-io gadget is used to visualize the containers generating the most block device input/output.
On Kubernetes
First, we need to create one pod for us to play with:
$ kubectl run test-pod --image busybox:latest sleep inf
You can now use the gadget, but output will be empty:
$ kubectl gadget top block-io
K8S.NODE K8S.NAMESPACE K8S.POD K8S.CONTAINER PID COMM R/W MAJOR MINOR BYTES TIME(µs) IOs
Indeed, it is waiting for I/O to occur.
So, open another terminal and keep and eye on the first one, exec the container and use dd:
$ kubectl exec -ti test-pod -- dd if=/dev/zero of=/tmp/foo count=16384
On the first terminal, you should see:
K8S.NODE K8S.NAMESPACE K8S.POD K8S.CONTAINER PID COMM R/W MAJOR MINOR BYTES TIME(µs) IOs
minikube default test-pod test-pod 7767 dd W 0 0 1564672 3046 4
This line correspond to the block device I/O initiated by dd.
Clean everything
Congratulations! You reached the end of this guide! You can now delete the pod you created:
$ kubectl delete pod test-pod
pod "test-pod" deleted
With ig
Start a container that performs some IO activity:
$ docker run --rm --name test-top-block-io busybox /bin/sh -c'while true; do dd if=/dev/zero of=/tmp/foo count=4096; sync; done'
Start the gadget on another terminal and you’ll see the activity produced by the test-top-block-io container.
$ sudo ig top block-io -c test-top-block-io
RUNTIME.CONTAINERNAME PID COMM R/W MAJOR MINOR BYTES TIME OPS
test-top-block-io 63666 sync W 253 0 24576 428 5
test-top-block-io 63715 dd W 253 0 2097152 4816 5
...