Common Issues

Many of these problem cases are hard to summarize down to a short phrase that adequately describes the problem. Each problem will start with a bulleted list of symptoms. Keep in mind that all symptoms may not apply depending upon the configuration of the Rook. If the majority of the symptoms are seen there is a fair chance you are experiencing that problem.

If after trying the suggestions found on this page and the problem is not resolved, the Rook team is very happy to help you troubleshoot the issues in their Slack channel. Once you have registered for the Rook Slack, proceed to the General channel to ask for assistance.

Table of Contents

• Troubleshooting Techniques
• Pod using Rook storage is not running
• Cluster failing to service requests
• Only a single monitor pod starts
• OSD pods are failing to start
• OSDs are not created on my devices
• Node hangs after reboot
• Rook Agent modprobe exec format error
• Using multiple shared filesystem (CephFS) is attempted on a kernel version older than 4.7

Troubleshooting Techniques

There are two main categories of information you will need to investigate issues in the cluster:

1. Kubernetes status and logs
2. Ceph status

Kubernetes Tools

Kubernetes status is the first line of investigating when something goes wrong with the cluster. Here are a few artifacts that are helpful to gather:

• Rook pod status:
  • kubectl get pod -n rook-ceph -o wide
  • kubectl get pod -n rook-ceph-system -o wide
• Logs for Rook pods
  • Logs for the operator: kubectl logs -n rook-ceph-system -l app=rook-operator
  • Logs for a specific pod: kubectl logs -n rook-ceph <pod-name>, or a pod using a label such as mon1: kubectl logs -n rook-ceph -l mon=rook-ceph-mon1
  • Logs on a specific node to find why a PVC is failing to mount:
    • Rook agent errors around the attach/detach: kubectl logs -n rook-ceph-system <rook-ceph-agent-pod>
    • Connect to the node, then get kubelet logs (if your distro is using systemd): journalctl -u kubelet
  • See the log collection topic for a script that will help you gather the logs
• Other Rook artifacts:
  • The monitors that are expected to be in quorum: kubectl -n rook-ceph get configmap rook-ceph-mon-endpoints -o yaml | grep data
  • More artifacts in the rook namespace: kubectl -n rook-ceph get all

Ceph Tools

After you verify the basic health of the running pods, next you will want to run Ceph tools for status of the storage components. There are two ways to run the Ceph tools, either in the Rook toolbox or inside other Rook pods that are already running.

Tools in the Rook Toolbox

The rook-ceph-tools pod is a one-stop shop for both Ceph tools and other troubleshooting tools. Once the pod is up and running one connect to the pod to execute Ceph commands to evaluate that current state of the cluster.

 kubectl exec -it rook-ceph-tools bash

Tools in other pods

The Ceph tools are found in all of the Rook pods where Ceph is running, such as the operator and monitors. Rather than starting the toolbox pod, you can connect to the existing pods to more quickly execute the Ceph tools. For example, to connect to the operator pod:

kubectl -n rook-ceph-system exec -it $(kubectl -n rook-ceph-system get pods -l app=rook-operator -o jsonpath='{.items[0].metadata.name}') -- bash

Now from inside the operator pod you can execute the Ceph tools.

It is preferred to connect to the operator pod rather than monitors since the operator always has the latest configuration files. If you have multiple Rook clusters, it is preferred to connect to the Rook toolbox for a specific cluster. Otherwise, your ceph commands may connect to the wrong cluster.

Ceph Commands

Here are some common commands to troubleshoot the cluster.

• ceph status
• ceph osd status
• ceph osd df
• ceph osd utilization
• ceph osd pool stats
• ceph osd tree
• ceph pg stat

The first two status commands provide the overall cluster health. The normal state for cluster operations is HEALTH_OK, but will still function when the state is in a HEALTH_WARN state. If you are in a WARN state, then the cluster is in a condition that it may enter the HEALTH_ERROR state at which point all disk I/O operations are halted. If a HEALTH_WARN state is observed, then one should take action to prevent the cluster from halting when it enters the HEALTH_ERROR state.

There are many Ceph sub-commands to look at and manipulate Ceph objects, well beyond the scope this document. See the Ceph documentation for more details of gathering information about the health of the cluster. In addition, there are other helpful hints and some best practices located in the Advanced Configuration section. Of particular note there are scripts for collecting logs and gathering OSD information there.

Pod Using Rook Storage Is Not Running

Symptoms

• The pod that is configured to use Rook storage is stuck in the ContainerCreating status
• kubectl describe pod for the pod mentions one or more of the following:
  • PersistentVolumeClaim is not bound
  • timeout expired waiting for volumes to attach/mount
• kubectl -n rook-ceph-system get pod shows the rook-ceph-agent pods in a CrashLoopBackOff status

Possible Solutions Summary

• rook-ceph-agent pod is in a CrashLoopBackOff status because it cannot deploy its driver on a read-only filesystem: Flexvolume configuration pre-reqs
• Persistent Volume and/or Claim are failing to be created and bound: Volume Creation
• rook-ceph-agent pod is failing to mount and format the volume: Rook Agent Mounting
• You are using Kubernetes 1.7.x or earlier and the Kubelet has not been restarted after rook-ceph-agent is in the Running status: Restart Kubelet

Investigation Details

If you see some of the symptoms above, it’s because the requested Rook storage for your pod is not being created and mounted successfully. In this walkthrough, we will be looking at the wordpress mysql example pod that is failing to start. To first confirm there is an issue, you can run commands similar to the following and you should see similar output (note that some of it has been omitted for brevity):

> kubectl get pod
NAME                              READY     STATUS              RESTARTS   AGE
wordpress-mysql-918363043-50pjr   0/1       ContainerCreating   0          1h

> kubectl describe pod wordpress-mysql-918363043-50pjr
...
Events:
  FirstSeen	LastSeen	Count	From			SubObjectPath	Type		Reason			Message
  ---------	--------	-----	----			-------------	--------	------			-------
  1h		1h		3	default-scheduler			Warning		FailedScheduling	PersistentVolumeClaim is not bound: "mysql-pv-claim" (repeated 2 times)
  1h		35s		36	kubelet, 172.17.8.101			Warning		FailedMount		Unable to mount volumes for pod "wordpress-mysql-918363043-50pjr_default(08d14e75-bd99-11e7-bc4c-001c428b9fc8)": timeout expired waiting for volumes to attach/mount for pod "default"/"wordpress-mysql-918363043-50pjr". list of unattached/unmounted volumes=[mysql-persistent-storage]
  1h		35s		36	kubelet, 172.17.8.101			Warning		FailedSync		Error syncing pod

To troubleshoot this, let’s walk through the volume provisioning steps in order to confirm where the failure is happening.

Rook Agent Deployment

The rook-ceph-agent pods are responsible for mapping and mounting the volume from the cluster onto the node that your pod will be running on. If the rook-ceph-agent pod is not running then it cannot perform this function. Below is an example of the rook-ceph-agent pods failing to get to the Running status because they are in a CrashLoopBackOff status:

> kubectl -n rook-ceph-system get pod
NAME                                  READY     STATUS             RESTARTS   AGE
rook-ceph-agent-ct5pj                 0/1       CrashLoopBackOff   16         59m
rook-ceph-agent-zb6n9                 0/1       CrashLoopBackOff   16         59m
rook-operator-2203999069-pmhzn        1/1       Running            0          59m

If you see this occurring, you can get more details about why the rook-ceph-agent pods are continuing to crash with the following command and its sample output:

> kubectl -n rook-ceph-system get pod -l app=rook-ceph-agent -o jsonpath='{range .items[*]}{.metadata.name}{"\t"}{.status.containerStatuses[0].lastState.terminated.message}{"\n"}{end}'
rook-ceph-agent-ct5pj	mkdir /usr/libexec/kubernetes: read-only file system
rook-ceph-agent-zb6n9	mkdir /usr/libexec/kubernetes: read-only file system

From the output above, we can see that the agents were not able to bind mount to /usr/libexec/kubernetes on the host they are scheduled to run on. For some environments, this default path is read-only and therefore a better path must be provided to the agents.

First, clean up the agent deployment with:

kubectl -n rook-ceph-system delete daemonset rook-ceph-agent

Once the rook-ceph-agent pods are gone, follow the instructions in the Flexvolume configuration pre-reqs to ensure a good value for --volume-plugin-dir has been provided to the Kubelet. After that has been configured, and the Kubelet has been restarted, start the agent pods up again by restarting rook-operator:

kubectl -n rook-ceph-system delete pod -l app=rook-operator

Kubelet Restart

Kubernetes 1.7.x only

If the rook-ceph-agent pods are all in the Running state then another thing to confirm is that if you are running on Kubernetes 1.7.x, the Kubelet must be restarted after the rook-ceph-agent pods are running.

A symptom of this can be found in the Kubelet’s log/journal, with the following error saying no volume plugin matched:

Oct 30 22:23:03 core-02 kubelet-wrapper[31926]: E1030 22:23:03.524159   31926 desired_state_of_world_populator.go:285] Failed to add volume "mysql-persistent-storage" (specName: "pvc-9f273fbc") for pod "9f2ff89a-bdbf" to desiredStateOfWorld. err=failed to get Plugin from volumeSpec for volume "pvc-9f273fbc" err=no volume plugin matched

If you encounter this, just restart the Kubelet process, as described in the Restart Kubelet section of the Rook deployment guide.

Volume Creation

The volume must first be created in the Rook cluster and then bound to a volume claim before it can be mounted to a pod. Let’s confirm that with the following commands and their output:

> kubectl get pv
NAME                                       CAPACITY   ACCESSMODES   RECLAIMPOLICY   STATUS     CLAIM                    STORAGECLASS   REASON    AGE
pvc-9f273fbc-bdbf-11e7-bc4c-001c428b9fc8   20Gi       RWO           Delete          Bound      default/mysql-pv-claim   rook-ceph-block               25m

> kubectl get pvc
NAME             STATUS    VOLUME                                     CAPACITY   ACCESSMODES   STORAGECLASS   AGE
mysql-pv-claim   Bound     pvc-9f273fbc-bdbf-11e7-bc4c-001c428b9fc8   20Gi       RWO           rook-ceph-block     25m

Both your volume and its claim should be in the Bound status. If one or neither of them is not in the Bound status, then look for details of the issue in the rook-operator logs:

kubectl -n rook-ceph-system logs `kubectl -n rook-ceph-system -l app=rook-operator get pods -o jsonpath='{.items[*].metadata.name}'`

If the volume is failing to be created, there should be details in the rook-operator log output, especially those tagged with op-provisioner.

One common cause for the rook-operator failing to create the volume is when the clusterNamespace field of the StorageClass doesn’t match the namespace of the Rook cluster, as described in #1502. In that scenario, the rook-operator log would show a failure similar to the following:

2018-03-28 18:58:32.041603 I | op-provisioner: creating volume with configuration {pool:replicapool clusterNamespace:rook-ceph fstype:}
2018-03-28 18:58:32.041728 I | exec: Running command: rbd create replicapool/pvc-fd8aba49-32b9-11e8-978e-08002762c796 --size 20480 --cluster=rook --conf=/var/lib/rook/rook-ceph/rook.config --keyring=/var/lib/rook/rook-ceph/client.admin.keyring
E0328 18:58:32.060893       5 controller.go:801] Failed to provision volume for claim "default/mysql-pv-claim" with StorageClass "rook-ceph-block": Failed to create rook block image replicapool/pvc-fd8aba49-32b9-11e8-978e-08002762c796: failed to create image pvc-fd8aba49-32b9-11e8-978e-08002762c796 in pool replicapool of size 21474836480: Failed to complete '': exit status 1. global_init: unable to open config file from search list /var/lib/rook/rook-ceph/rook.config
. output:

The solution is to ensure that the clusterNamespace field matches the namespace of the Rook cluster when creating the StorageClass.

Volume Mounting

The final step in preparing Rook storage for your pod is for the rook-ceph-agent pod to mount and format it. If all the preceding sections have been successful or inconclusive, then take a look at the rook-ceph-agent pod logs for further clues. You can determine which rook-ceph-agent is running on the same node that your pod is scheduled on by using the -o wide output, then you can get the logs for that rook-ceph-agent pod similar to the example below:

> kubectl -n rook-ceph-system get pod -o wide
NAME                                  READY     STATUS    RESTARTS   AGE       IP             NODE
rook-ceph-agent-h6scx                 1/1       Running   0          9m        172.17.8.102   172.17.8.102
rook-ceph-agent-mp7tn                 1/1       Running   0          9m        172.17.8.101   172.17.8.101
rook-operator-2203999069-3tb68        1/1       Running   0          9m        10.32.0.7      172.17.8.101

> kubectl -n rook-ceph-system logs rook-ceph-agent-h6scx
2017-10-30 23:07:06.984108 I | rook: starting Rook v0.5.0-241.g48ce6de.dirty with arguments '/usr/local/bin/rook agent'
...

In the rook-ceph-agent pod logs, you may see a snippet similar to the following:

Failed to complete rbd: signal: interrupt.

In this case, the agent waited for the rbd command but it did not finish in a timely manner so the agent gave up and stopped it. This can happen for multiple reasons, but using dmesg will likely give you insight into the root cause. If dmesg shows something similar to below, then it means you have an old kernel that can’t talk to the cluster:

libceph: mon2 10.205.92.13:6790 feature set mismatch, my 4a042a42 < server's 2004a042a42, missing 20000000000

If uname -a shows that you have a kernel version older than 3.15, you’ll need to perform one of the following:

• Disable some Ceph features by starting the rook toolbox and running ceph osd crush tunables bobtail
• Upgrade your kernel to 3.15 or later.

Filesystem Mounting

In the rook-ceph-agent pod logs, you may see a snippet similar to the following:

2017-11-07 00:04:37.808870 I | rook-flexdriver: WARNING: The node kernel version is 4.4.0-87-generic, which do not support multiple ceph filesystems. The kernel version has to be at least 4.7. If you have multiple ceph filesystems, the result could be inconsistent

This will happen in kernels with versions older than 4.7, where the option mds_namespace is not supported. This option is used to specify a filesystem namespace.

In this case, if there is only one filesystem in the Rook cluster, there should be no issues and the mount should succeed. If you have more than one filesystem, inconsistent results may arise and the filesystem mounted may not be the one you specified.

If the issue is still not resolved from the steps above, please come chat with us on the #general channel of our Rook Slack. We want to help you get your storage working and learn from those lessons to prevent users in the future from seeing the same issue.

Cluster failing to service requests

Symptoms

• Execution of the ceph command hangs
• PersistentVolumes are not being created
• Large amount of slow requests are blocking
• Large amount of stuck requests are blocking
• One or more MONs are restarting periodically

Investigation

Create a rook-ceph-tools pod to investigate the current state of CEPH. Here is an example of what one might see. In this case the ceph status command would just hang so a CTRL-C needed to be sent.

$ kubectl -n rook-ceph exec -it rook-ceph-tools bash
root@rook-ceph-tools:/# ceph status
^CCluster connection interrupted or timed out

Another indication is when one or more of the MON pods restart frequently. Note the ‘mon107’ that has only been up for 16 minutes in the following output.

$ kubectl -n rook-ceph get all -o wide --show-all
NAME                                 READY     STATUS    RESTARTS   AGE       IP               NODE
po/rook-ceph-mgr0-2487684371-gzlbq   1/1       Running   0          17h       192.168.224.46   k8-host-0402
po/rook-ceph-mon107-p74rj            1/1       Running   0          16m       192.168.224.28   k8-host-0402
rook-ceph-mon1-56fgm                 1/1       Running   0          2d        192.168.91.135   k8-host-0404
rook-ceph-mon2-rlxcd                 1/1       Running   0          2d        192.168.123.33   k8-host-0403
rook-ceph-osd-bg2vj                  1/1       Running   0          2d        192.168.91.177   k8-host-0404
rook-ceph-osd-mwxdm                  1/1       Running   0          2d        192.168.123.31   k8-host-0403

Solution

What is happening here is that the MON pods are restarting and one or more of the Ceph daemons are not getting configured with the proper cluster information. This is commonly the result of not specifying a value for dataDirHostPath in your Cluster CRD.

The dataDirHostPath setting specifies a path on the local host for the CEPH daemons to store configuration and data. Setting this to a path like /var/lib/rook, reapplying your Cluster CRD and restarting all the CEPH daemons (MON, MGR, OSD, RGW) should solve this problem. After the CEPH daemons have been restarted, it is advisable to restart the rook-tool pod.

Only a single monitor pod starts

Symptoms

• Rook operator is running
• Only one mon pod is running

Investigation

When the operator is starting a cluster, the operator will start one mon at a time and check that they are healthy before continuing to bring up all three mons. If the first mon is not detected healthy, the operator will continue to check until it is healthy. There are two likely causes for the mon health not being detected:

• The operator pod does not have network connectivity to the mon pod
• The mon pod is failing to start

Operator fails to connect to the mon

First look at the logs of the operator to confirm if it is able to connect to the mons.

$ kubectl -n rook-ceph-system logs -l app=rook-operator

Likely you will see an error similar to the following that the operator is timing out when connecting to the mon. The last command is ceph mon_status, followed by a timeout message five minutes later.

2018-01-21 21:47:32.375833 I | exec: Running command: ceph mon_status --cluster=rook --conf=/var/lib/rook/rook-ceph/rook.config --keyring=/var/lib/rook/rook-ceph/client.admin.keyring --format json --out-file /tmp/442263890
2018-01-21 21:52:35.370533 I | exec: 2018-01-21 21:52:35.071462 7f96a3b82700  0 monclient(hunting): authenticate timed out after 300
2018-01-21 21:52:35.071462 7f96a3b82700  0 monclient(hunting): authenticate timed out after 300
2018-01-21 21:52:35.071524 7f96a3b82700  0 librados: client.admin authentication error (110) Connection timed out
2018-01-21 21:52:35.071524 7f96a3b82700  0 librados: client.admin authentication error (110) Connection timed out
[errno 110] error connecting to the cluster

The error would appear to be an authentication error, but it is misleading. The real issue is a timeout.

Solution

If you see the timeout in the operator log, verify if the mon pod is running (see the next section). If the mon pod is running, check the network connectivity between the operator pod and the mon pod. A common issue is that the CNI is not configured correctly.

Failing mon pod

Second we need to verify if the mon pod started successfully.

$ kubectl -n rook-ceph get pod -l app=rook-ceph-mon
NAME                   READY     STATUS             RESTARTS   AGE
rook-ceph-mon0-r8tbl   0/1       CrashLoopBackOff   2          47s

If the mon pod is failing as in this example, you will need to look at the mon pod status or logs to determine the cause. If the pod is in a crash loop backoff state, you should see the reason by describing the pod.

# the pod shows a termination status that the keyring does not match the existing keyring
$ kubectl -n rook-ceph describe pod -l mon=rook-ceph-mon0
...
    Last State:		Terminated
      Reason:		Error
      Message:		The keyring does not match the existing keyring in /var/lib/rook/rook-ceph-mon0/data/keyring.
                    You may need to delete the contents of dataDirHostPath on the host from a previous deployment.
...

Solution

This is a common problem reinitializing the Rook cluster when the local directory used for persistence has not been purged. This directory is the dataDirHostPath setting in the cluster CRD and is typically set to /var/lib/rook. To fix the issue you will need to delete all components of Rook and then delete the contents of /var/lib/rook (or the directory specified by dataDirHostPath) on each of the hosts in the cluster. Then when the cluster CRD is applied to start a new cluster, the rook-operator should start all the pods as expected.

Important: Deleting the dataDirHostPath folder is destructive to the storage. Only delete the folder if you are trying to permanently purge the Rook cluster.

OSD pods are failing to start

Symptoms

• OSD pods are failing to start
• You have started a cluster after tearing down another cluster

Investigation

When an OSD starts, the device or directory will be configured for consumption. If there is an error with the configuration, the pod will crash and you will see the CrashLoopBackoff status for the pod. Look in the osd pod logs for an indication of the failure.

$ kubectl -n rook-ceph logs rook-ceph-osd-fl8fs
...

One common case for failure is that you have re-deployed a test cluster and some state may remain from a previous deployment. If your cluster is larger than a few nodes, you may get lucky enough that the monitors were able to start and form quorum. However, now the OSDs pods may fail to start due to the old state. Looking at the OSD pod logs you will see an error about the file already existing.

$ kubectl -n rook-ceph logs rook-ceph-osd-fl8fs
...
2017-10-31 20:13:11.187106 I | mkfs-osd0: 2017-10-31 20:13:11.186992 7f0059d62e00 -1 bluestore(/var/lib/rook/osd0) _read_fsid unparsable uuid
2017-10-31 20:13:11.187208 I | mkfs-osd0: 2017-10-31 20:13:11.187026 7f0059d62e00 -1 bluestore(/var/lib/rook/osd0) _setup_block_symlink_or_file failed to create block symlink to /dev/disk/by-partuuid/651153ba-2dfc-4231-ba06-94759e5ba273: (17) File exists
2017-10-31 20:13:11.187233 I | mkfs-osd0: 2017-10-31 20:13:11.187038 7f0059d62e00 -1 bluestore(/var/lib/rook/osd0) mkfs failed, (17) File exists
2017-10-31 20:13:11.187254 I | mkfs-osd0: 2017-10-31 20:13:11.187042 7f0059d62e00 -1 OSD::mkfs: ObjectStore::mkfs failed with error (17) File exists
2017-10-31 20:13:11.187275 I | mkfs-osd0: 2017-10-31 20:13:11.187121 7f0059d62e00 -1  ** ERROR: error creating empty object store in /var/lib/rook/osd0: (17) File exists

Solution

If the error is from the file that already exists, this is a common problem reinitializing the Rook cluster when the local directory used for persistence has not been purged. This directory is the dataDirHostPath setting in the cluster CRD and is typically set to /var/lib/rook. To fix the issue you will need to delete all components of Rook and then delete the contents of /var/lib/rook (or the directory specified by dataDirHostPath) on each of the hosts in the cluster. Then when the cluster CRD is applied to start a new cluster, the rook-operator should start all the pods as expected.

OSD pods are not created on my devices

Symptoms

• No OSD pods are started in the cluster
• Devices are not configured with OSDs even though specified in the Cluster CRD
• One OSD pod is started on each node instead of multiple pods for each device

Investigation

First, ensure that you have specified the devices correctly in the CRD. The Cluster CRD has several ways to specify the devices that are to be consumed by the Rook storage:

• useAllDevices: true: Rook will consume all devices it determines to be available
• deviceFilter: Consume all devices that match this regular expression
• devices: Explicit list of device names on each node to consume

Second, if Rook determines that a device is not available (has existing partitions or a formatted file system), Rook will skip consuming the devices. If Rook is not starting OSDs on the devices you expect, Rook may have skipped it for this reason. To see if a device was skipped, view the OSD preparation log on the node where the device was skipped.

# get the prepare pods in the cluster
$ kubectl -n rook-ceph get pod -l app=rook-ceph-osd-prepare
NAME                                   READY     STATUS      RESTARTS   AGE
rook-ceph-osd-prepare-node1-fvmrp      0/1       Completed   0          18m
rook-ceph-osd-prepare-node2-w9xv9      0/1       Completed   0          22m
rook-ceph-osd-prepare-node3-7rgnv      0/1       Completed   0          22m

# view the logs for the node of interest
$ kubectl -n rook-ceph logs rook-ceph-osd-prepare-node1-fvmrp

Towards the begining of the log you will see messages such as the following:

# message that the device sda was skipped
cephosd: skipping device sda that is in use (not by rook)

# message that the devices sdb and sdc are being configured
cephosd: configuring osd devices: {"Entries":{"sdb":{"Data":-1,"Metadata":null},"sdc":{"Data":-1,"Metadata":null}}}

Solution

After you have either updated the CRD with the correct settings, or you have cleaned the partitions or file system from your devices, you can trigger the operator to analyze the devices again by restarting the operator. Each time the operator starts, it will ensure all the desired devices are configured.

# Restart the operator to ensure devices are configured. A new pod will automatically be started when the current operator pod is deleted.
$ kubectl -n rook-ceph-system delete pod -l app=rook-ceph-operator

Node hangs after reboot

Symptoms

• After issuing a reboot command, node never returned online
• Only a power cycle helps

Solution

The node needs to be drained before reboot. After the successful drain, the node can be rebooted as usual.

Because kubectl drain command automatically marks the node as unschedulable (kubectl cordon effect), the node needs to be uncordoned once it’s back online.

Drain the node:

$ kubectl drain <node-name> --ignore-daemonsets --delete-local-data

Uncordon the node:

kubectl uncordon <node-name>

Rook Agent modprobe exec format error

Symptoms

• PersistentVolumes from Ceph fail/timeout to mount
• Rook Agent logs contain modinfo: ERROR: could not get modinfo from 'rbd': Exec format error lines

Solution

If it is feasible to upgrade your kernel, you should upgrade to 4.x, even better is >= 4.7 due to a feature for CephFS added to the kernel.

If you are unable to upgrade the kernel, you need to go to each host that will consume storage and run:

modprobe rbd

This command inserts the rbd module into the kernel.

To persist this fix, you need to add the rbd kernel module to either /etc/modprobe.d/ or /etc/modules-load.d/. For both paths create a file called rbd.conf with the following content:

rbd

Now when a host is restarted, the module should be loaded automatically.

Using multiple shared filesystem (CephFS) is attempted on a kernel version older than 4.7

Symptoms

• More than one shared filesystem (CephFS) has been created in the cluster
• A pod attempts to mount any other shared filesystem besides the first one that was created
• The pod incorrectly gets the first filesystem mounted instead of the intended filesystem

Solution

The only solution to this problem is to upgrade your kernel to 4.7 or higher. This is due to a mount flag added in the kernel version 4.7 which allows to chose the filesystem by name.

For additional info on the kernel version requirement for multiple shared filesystems (CephFS), see Filesystem - Kernel version requirement.