7.3. Ceph
Poor performance of the stretch clusters on CephFS
Workloads with many small metadata operations might exhibit poor performance because of the arbitrary placement of metadata server (MDS) on multi-site Data Foundation clusters.
SELinux relabelling issue with a very high number of files
When attaching volumes to pods in Red Hat OpenShift Container Platform, the pods sometimes do not start or take an excessive amount of time to start. This behavior is generic and it is tied to how SELinux relabelling is handled by the Kubelet. This issue is observed with any filesystem based volumes having very high file counts. In OpenShift Data Foundation, the issue is seen when using CephFS based volumes with a very high number of files. There are different ways to workaround this issue. Depending on your business needs you can choose one of the workarounds from the knowledgebase solution https://access.redhat.com/solutions/6221251.
Ceph reports
no active mgrafter workload deploymentAfter workload deployment, Ceph manager loses connectivity to MONs or is unable to respond to its liveness probe.
This causes the OpenShift Data Foundation cluster status to report that there is "no active mgr". This causes multiple operations that use the Ceph manager for request processing to fail. For example, volume provisioning, creating CephFS snapshots, and others.
To check the status of the OpenShift Data Foundation cluster, use the command
oc get cephcluster -n openshift-storage. In the status output, thestatus.ceph.details.MGR_DOWNfield will have the message "no active mgr" if your cluster has this issue.Workaround: Restart the Ceph manager pods using the following commands:
# oc scale deployment -n openshift-storage rook-ceph-mgr-a --replicas=0# oc scale deployment -n openshift-storage rook-ceph-mgr-a --replicas=1After running these commands, the OpenShift Data Foundation cluster status reports a healthy cluster, with no warnings or errors regarding
MGR_DOWN.
CephBlockPool creation fails when custom deviceClass is used in StorageCluster
Due to a known issue, CephBlockPool creation fails when custom deviceClass is used in StorageCluster.
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