Chapter 9. Reclaiming space on target volumes

The deleted files or chunks of zero data Sometimes take up storage space on the Ceph cluster resulting in inaccurate reporting of the available storage space. The reclaim space operation removes such discrepancies by executing the following operations on the target volume:

  • fstrim - This operation is executed on volumes that are in Filesystem mode and only if the volume is mounted to a pod at the time of execution of reclaim space operation.
  • rbd sparsify - This operation is executed when the volume is not attached to any pods and reclaims the space occupied by chunks of 4M-sized zeroed data.
Note
  • The reclaim space operation is supported only by the Ceph RBD volumes.
  • The reclaim space operation involves a performance penalty when it is being executed.

For upgraded clusters, execute the following command before you proceed further. 

$ oc patch cm rook-ceph-operator-config -n openshift-storage -p $'data:\n "CSI_ENABLE_CSIADDONS": "true”'

You can use one of the following methods to reclaim the space:

  • Enabling reclaim space operation using Annotating PersistentVolumeClaims (Recommended method to use for enabling reclaim space operation)
  • Enabling reclaim space operation using ReclaimSpaceJob
  • Enabling reclaim space operation using ReclaimSpaceCronJob

9.1. Enabling reclaim space operation using Annotating PersistentVolumeClaims

Use this procedure to annotate PersistentVolumeClaims so that it can invoke the reclaim space operation automatically based on a given schedule.

Note
  • The schedule value is in the same format as the Kubernetes CronJobs which sets the and/or interval of the recurring operation request.
  • Recommended schedule interval is @weekly. If the schedule interval value is empty or in an invalid format, then the default schedule value is set to @weekly.
  • Minimum supported interval between each scheduled operation is at least 24 hours. For example, @daily (At 00:00 every day) or 0 3 * * * (At 3:00 every day).
  • Schedule the ReclaimSpace operation during off-peak, maintenance window, or the interval when the workload input/output is expected to be low.
  • ReclaimSpaceCronJob is recreated when the schedule is modified. It is automatically deleted when the annotation is removed.

Procedure

  1. Get the persistent volume claim (PVC) details. 

    $ oc get pvc data-pvc
    NAME      STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS                          AGE
data-pvc  Bound    pvc-f37b8582-4b04-4676-88dd-e1b95c6abf74   1Gi        RWO            ocs-storagecluster-ceph-rbd           20h

  2. Add annotation reclaimspace.csiaddons.openshift.io/schedule=@monthly to the PVC to create reclaimspacecronjob. 

    $ oc annotate pvc data-pvc "reclaimspace.csiaddons.openshift.io/schedule=@monthly"
    persistentvolumeclaim/data-pvc annotated

  3. Verify that reclaimspacecronjob is created in the format, "<pvc-name>-xxxxxxx". 

    $ oc get reclaimspacecronjobs.csiaddons.openshift.io
    NAME                    SCHEDULE    SUSPEND   ACTIVE   LASTSCHEDULE   AGE
data-pvc-1642663516     @monthly                                      3s

  4. Modify the schedule to run this job automatically. 

    $ oc annotate pvc data-pvc "reclaimspace.csiaddons.openshift.io/schedule=@weekly" --overwrite=true
    persistentvolumeclaim/data-pvc annotated

  5. Verify that the schedule for reclaimspacecronjob has been modified. 

    $ oc get reclaimspacecronjobs.csiaddons.openshift.io
    NAME                  SCHEDULE    SUSPEND   ACTIVE   LASTSCHEDULE   AGE
data-pvc-1642664617   @weekly                                       3s

9.2. Enabling reclaim space operation using ReclaimSpaceJob

ReclaimSpaceJob is a namespaced custom resource (CR) designed to invoke reclaim space operation on the target volume. This is a one time method that immediately starts the reclaim space operation. You have to repeat the creation of ReclaimSpaceJob CR to repeat the reclaim space operation when required.

Note
  • Recommended interval between the reclaim space operations is weekly.
  • Ensure that the minimum interval between each operation is at least 24 hours.
  • Schedule the reclaim space operation during off-peak, maintenance window, or when the workload input/output is expected to be low.

Procedure

  1. Create and apply the following custom resource for reclaim space operation: 

    apiVersion: csiaddons.openshift.io/v1alpha1
kind: ReclaimSpaceJob
metadata:
  name: sample-1
spec:
  target:
    persistentVolumeClaim: pvc-1

    where,

    target
    Indicates the volume target on which the operation is performed.
    persistentVolumeClaim
    Name of the PersistentVolumeClaim.
    backOfflimit
    Specifies the maximum number of retries before marking the reclaim space operation as failed. The default value is 6. The allowed maximum and minimum values are 60 and 0 respectively.
    retryDeadlineSeconds
    Specifies the duration in which the operation might retire in seconds and it is relative to the start time. The value must be a positive integer. The default value is 600 seconds and the allowed maximum value is 1800 seconds.
  2. Delete the custom resource after completion of the operation.

9.3. Enabling reclaim space operation using ReclaimSpaceCronJob

ReclaimSpaceCronJob invokes the reclaim space operation based on the given schedule such as daily, weekly, and so on. You have to create ReclaimSpaceCronJob only once for a persistent volume claim. The CSI-addons controller creates a ReclaimSpaceJob at the requested time and interval with the schedule attribute.

Note
  • Recommended schedule interval is @weekly.
  • Minimum interval between each scheduled operation should be at least 24 hours. For example, @daily (At 00:00 every day) or “0 3 * * *” (At 3:00 every day).
  • Schedule the ReclaimSpace operation during off-peak, maintenance window, or the interval when workload input/output is expected to be low.

Procedure

  1. Create and apply the following custom resource for reclaim space operation 

    apiVersion: csiaddons.openshift.io/v1alpha1
kind: ReclaimSpaceCronJob
metadata:
  name: reclaimspacecronjob-sample
spec:
  jobTemplate:
    spec:
      target:
        persistentVolumeClaim: data-pvc
  schedule: '@weekly'
  concurrencyPolicy: Forbid

    where,

    concurrencyPolicy
    Describes the changes when a new ReclaimSpaceJob is scheduled by the ReclaimSpaceCronJob, while a previous ReclaimSpaceJob is still running. The default Forbid prevents starting a new job whereas Replace can be used to delete the running job potentially in a failure state and create a new one.
    failedJobsHistoryLimit
    Specifies the number of failed ReclaimSpaceJobs that are kept for troubleshooting.
    jobTemplate
    Specifies the ReclaimSpaceJob.spec structure that describes the details of the requested ReclaimSpaceJob operation.
    successfulJobsHistoryLimit
    Specifies the number of successful ReclaimSpaceJob operations.
    schedule
    Specifieds the and/or interval of the recurring operation request and it is in the same format as the Kubernetes CronJobs.
  2. Delete the ReclaimSpaceCronJob custom resource when execution of reclaim space operation is no longer needed or when the target PVC is deleted.