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Applies to SUSE Enterprise Storage 7

8 Ceph OSD management Edit source

8.1 Ceph OSD management Edit source

Ceph Object Storage Daemons (OSDs) are the heart and soul of the Ceph storage platform. Each OSD manages a local device and together they provide the distributed storage. Rook will automate creation and management of OSDs to hide the complexity based on the desired state in the CephCluster CR as much as possible. This guide will walk through some of the scenarios to configure OSDs where more configuration may be required.

8.1.1 Analyzing OSD health Edit source

The rook-ceph-tools pod provides a simple environment to run Ceph tools. The Ceph commands mentioned in this document should be run from the toolbox.

Once created, connect to the pod to execute the ceph commands to analyze the health of the cluster, in particular the OSDs and placement groups (PGs). Some common commands to analyze OSDs include:

cephuser@adm > ceph status
cephuser@adm > ceph osd tree
cephuser@adm > ceph osd status
cephuser@adm > ceph osd df
cephuser@adm > ceph osd utilization
kubectl -n rook-ceph exec -it $(kubectl -n rook-ceph get pod -l "app=rook-ceph-tools" -o jsonpath='{.items[0].metadata.name}') bash

8.1.2 Adding an OSD Edit source

To add more OSDs, Rook automatically watches for new nodes and devices being added to your cluster. If they match the filters or other settings in the storage section of the cluster CR, the operator will create new OSDs.

8.1.3 Adding an OSD on a PVC Edit source

In more dynamic environments where storage can be dynamically provisioned with a raw block storage provider, the OSDs can be backed by PVCs.

To add more OSDs, you can either increase the count of the OSDs in an existing device set or you can add more device sets to the cluster CR. The operator will then automatically create new OSDs according to the updated cluster CR.

8.1.4 Removing an OSD Edit source

Removal of OSDs is intentionally not automated. Rook’s charter is to keep your data safe, not to delete it. If you are sure you need to remove OSDs, it can be done. We just want you to be in control of this action.

To remove an OSD due to a failed disk or other re-configuration, consider the following to ensure the health of the data through the removal process:

  1. Confirm you will have enough space on your cluster after removing your OSDs to properly handle the deletion.

  2. Confirm the remaining OSDs and their placement groups (PGs) are healthy in order to handle the rebalancing of the data

  3. Do not remove too many OSDs at once, wait for rebalancing between removing multiple OSDs

  4. On host-based clusters, you may need to stop the Rook Operator while performing OSD removal steps in order to prevent Rook from detecting the old OSD and trying to re-create it before the disk is wiped or removed.

If all the PGs are active+clean and there are no warnings about being low on space, this means the data is fully replicated and it is safe to proceed. If an OSD is failing, the PGs will not be perfectly clean, and you will need to proceed anyway.

8.1.4.1 From the toolbox Edit source

  1. Determine the OSD ID for the OSD to be removed. The OSD pod may be in an error state, such as CrashLoopBackoff, or the ceph commands in the toolbox may show which OSD is down.

  2. Mark the OSD as out if not already marked as such by Ceph. This signals Ceph to start moving (backfilling) the data that was on that OSD to another OSD.

    ceph osd out osd.ID

    For example:

    cephuserceph osd out osd.23
  3. Wait for the data to finish backfilling to other OSDs.

    ceph status will indicate the backfilling is done when all of the PGs are active+clean. It’s safe to remove the disk after that.

  4. Update your CephCluster CR such that the operator will not create an OSD on the device anymore. Depending on your CR settings, you may need to remove the device from the list or update the device filter. If you are using useAllDevices: true, no change to the CR is necessary.

  5. Remove the OSD from the Ceph cluster

    cephuser@adm > ceph osd purge ID --yes-i-really-mean-it
  6. Verify the OSD is removed from the node in the CRUSH map:

    cephuser@adm > ceph osd tree

8.1.4.2 Removing the OSD deployment Edit source

The operator can automatically remove OSD deployments that are considered safe-to-destroy by Ceph. After the steps above, the OSD will be considered safe to remove since the data has all been moved to other OSDs. But this will only be done automatically by the operator if you have this setting in the cluster CR:

removeOSDsIfOutAndSafeToRemove: true

Otherwise, you will need to delete the deployment directly:

kubectl@adm > kubectl delete deployment -n rook-ceph rook-ceph-osd-ID

8.1.5 Replacing an OSD Edit source

To replace a disk that has failed:

  1. Run the steps in the previous section to Section 8.1.4, “Removing an OSD”.

  2. Replace the physical device and verify the new device is attached.

  3. Check if your cluster CR will find the new device. If you are using useAllDevices: true you can skip this step. If your cluster CR lists individual devices or uses a device filter you may need to update the CR.

  4. The operator ideally will automatically create the new OSD within a few minutes of adding the new device or updating the CR. If you do not see a new OSD automatically created, restart the operator (by deleting the operator pod) to trigger the OSD creation.

  5. Verify if the OSD is created on the node by running ceph osd tree from the toolbox.

Note
Note

The OSD might have a different ID than the previous OSD that was replaced.

8.1.6 Removing an OSD from a PVC Edit source

If you have installed your OSDs on top of PVCs and you desire to reduce the size of your cluster by removing OSDs:

  1. Shrink the number of OSDs in the storageClassDeviceSet in the CephCluster CR.

    kubectl@adm > kubectl -n rook-ceph edit cephcluster rook-ceph

    Reduce the count of the OSDs to the desired number. Rook will not take any action to automatically remove the extra OSD(s), but will effectively stop managing the orphaned OSD.

  2. Identify the orphaned PVC that belongs to the orphaned OSD.

    Note
    Note

    The orphaned PVC will have the highest index among the PVCs for the device set.

    kubectl@adm > kubectl -n rook-ceph get pvc -l ceph.rook.io/DeviceSet=deviceSet

    For example if the device set is named set1 and the count was reduced from 3 to 2, the orphaned PVC would have the index 2 and might be named set1-2-data-vbwcf

  3. Identify the orphaned OSD.

    Note
    Note

    The OSD assigned to the PVC can be found in the labels on the PVC.

    kubectl@adm > kubectl -n rook-ceph get pod -l ceph.rook.io/pvc=ORPHANED_PVC -o yaml | grep ceph-osd-id

    For example, this might return:

    cephuser@adm > ceph-osd-id: "0"
  4. Now proceed with the steps in the section above to Section 8.1.4, “Removing an OSD” for the orphaned OSD ID.

  5. If desired, delete the orphaned PVC after the OSD is removed.

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