PLEASE NOTE: This document applies to v1.2 version and not to the latest stable release v1.9

    Advanced Configuration

    These examples show how to perform advanced configuration tasks on your Rook storage cluster.


    Most of the examples make use of the ceph client command. A quick way to use the Ceph client suite is from a Rook Toolbox container.

    The Kubernetes based examples assume Rook OSD pods are in the rook-ceph namespace. If you run them in a different namespace, modify kubectl -n rook-ceph [...] to fit your situation.

    Use custom Ceph user and secret for mounting

    NOTE: For extensive info about creating Ceph users, consult the Ceph documentation: http://docs.ceph.com/docs/mimic/rados/operations/user-management/#add-a-user.

    Using a custom Ceph user and secret can be done for filesystem and block storage.

    Create a custom user in Ceph with read-write access in the /bar directory on CephFS (For Ceph Mimic or newer, use data=POOL_NAME instead of pool=POOL_NAME):

    ceph auth get-or-create-key client.user1 mon 'allow r' osd 'allow rw tag cephfs pool=YOUR_FS_DATA_POOL' mds 'allow r, allow rw path=/bar'

    The command will return a Ceph secret key, this key should be added as a secret in Kubernetes like this:

    kubectl create secret generic ceph-user1-secret --from-literal=key=YOUR_CEPH_KEY

    NOTE: This secret with the same name must be created in each namespace where the StorageClass will be used.

    In addition to this Secret you must create a RoleBinding to allow the Rook Ceph agent to get the secret from each namespace. The RoleBinding is optional if you are using a ClusterRoleBinding for the Rook Ceph agent secret access. A ClusterRole which contains the permissions which are needed and used for the Bindings are shown as an example after the next step.

    On a StorageClass parameters and/or flexvolume Volume entry options set the following options:

    mountUser: user1
    mountSecret: ceph-user1-secret

    If you want the Rook Ceph agent to require a mountUser and mountSecret to be set in StorageClasses using Rook, you must set the environment variable AGENT_MOUNT_SECURITY_MODE to Restricted on the Rook Ceph operator Deployment.

    For more information on using the Ceph feature to limit access to CephFS paths, see Ceph Documentation - Path Restriction.


    NOTE: When you are using the Helm chart to install the Rook Ceph operator and have set mountSecurityMode to e.g., Restricted, then the below ClusterRole has already been created for you.

    This ClusterRole is needed no matter if you want to use a RoleBinding per namespace or a ClusterRoleBinding.

    apiVersion: rbac.authorization.k8s.io/v1beta1
    kind: ClusterRole
      name: rook-ceph-agent-mount
        operator: rook
        storage-backend: ceph
    - apiGroups:
      - ""
      - secrets
      - get


    NOTE: You either need a RoleBinding in each namespace in which a mount secret resides in or create a ClusterRoleBinding with which the Rook Ceph agent has access to Kubernetes secrets in all namespaces.

    Create the RoleBinding shown here in each namespace the Rook Ceph agent should read secrets for mounting. The RoleBinding subjectsnamespace must be the one the Rook Ceph agent runs in (default rook-ceph for version 1.0 and newer. The default namespace in previous versions was rook-ceph-system).

    Replace namespace: name-of-namespace-with-mountsecret according to the name of all namespaces a mountSecret can be in.

    kind: RoleBinding
    apiVersion: rbac.authorization.k8s.io/v1beta1
      name: rook-ceph-agent-mount
      namespace: name-of-namespace-with-mountsecret
        operator: rook
        storage-backend: ceph
      apiGroup: rbac.authorization.k8s.io
      kind: ClusterRole
      name: rook-ceph-agent-mount
    - kind: ServiceAccount
      name: rook-ceph-system
      namespace: rook-ceph


    This ClusterRoleBinding only needs to be created once, as it covers the whole cluster.

    kind: ClusterRoleBinding
    apiVersion: rbac.authorization.k8s.io/v1beta1
      name: rook-ceph-agent-mount
        operator: rook
        storage-backend: ceph
      apiGroup: rbac.authorization.k8s.io
      kind: ClusterRole
      name: rook-ceph-agent-mount
    - kind: ServiceAccount
      name: rook-ceph-system
      namespace: rook-ceph

    Log Collection

    All Rook logs can be collected in a Kubernetes environment with the following command:

    (for p in $(kubectl -n rook-ceph get pods -o jsonpath='{.items[*].metadata.name}')
        for c in $(kubectl -n rook-ceph get pod ${p} -o jsonpath='{.spec.containers[*].name}')
            echo "BEGIN logs from pod: ${p} ${c}"
            kubectl -n rook-ceph logs -c ${c} ${p}
            echo "END logs from pod: ${p} ${c}"
    for i in $(kubectl -n rook-ceph-system get pods -o jsonpath='{.items[*].metadata.name}')
        echo "BEGIN logs from pod: ${i}"
        kubectl -n rook-ceph-system logs ${i}
        echo "END logs from pod: ${i}"
    done) | gzip > /tmp/rook-logs.gz

    This gets the logs for every container in every Rook pod and then compresses them into a .gz archive for easy sharing. Note that instead of gzip, you could instead pipe to less or to a single text file.

    OSD Information

    Keeping track of OSDs and their underlying storage devices/directories can be difficult. The following scripts will clear things up quickly.


    # Get OSD Pods
    # This uses the example/default cluster name "rook"
    OSD_PODS=$(kubectl get pods --all-namespaces -l \
      app=rook-ceph-osd,rook_cluster=rook-ceph -o jsonpath='{.items[*].metadata.name}')
    # Find node and drive associations from OSD pods
    for pod in $(echo ${OSD_PODS})
     echo "Pod:  ${pod}"
     echo "Node: $(kubectl -n rook-ceph get pod ${pod} -o jsonpath='{.spec.nodeName}')"
     kubectl -n rook-ceph exec ${pod} -- sh -c '\
      for i in /var/lib/rook/osd*; do
        [ -f ${i}/ready ] || continue
        echo -ne "-$(basename ${i}) "
        echo $(lsblk -n -o NAME,SIZE ${i}/block 2> /dev/null || \
        findmnt -n -v -o SOURCE,SIZE -T ${i}) $(cat ${i}/type)
      done | sort -V

    The output should look something like this. Note that OSDs on the same node will show duplicate information.

    Pod:  osd-m2fz2
    Node: node1.zbrbdl
    -osd0  sda3  557.3G  bluestore
    -osd1  sdf3  110.2G  bluestore
    -osd2  sdd3  277.8G  bluestore
    -osd3  sdb3  557.3G  bluestore
    -osd4  sde3  464.2G  bluestore
    -osd5  sdc3  557.3G  bluestore
    Pod:  osd-nxxnq
    Node: node3.zbrbdl
    -osd6   sda3  110.7G  bluestore
    -osd17  sdd3  1.8T    bluestore
    -osd18  sdb3  231.8G  bluestore
    -osd19  sdc3  231.8G  bluestore
    Pod:  osd-tww1h
    Node: node2.zbrbdl
    -osd7   sdc3  464.2G  bluestore
    -osd8   sdj3  557.3G  bluestore
    -osd9   sdf3  66.7G   bluestore
    -osd10  sdd3  464.2G  bluestore
    -osd11  sdb3  147.4G  bluestore
    -osd12  sdi3  557.3G  bluestore
    -osd13  sdk3  557.3G  bluestore
    -osd14  sde3  66.7G   bluestore
    -osd15  sda3  110.2G  bluestore
    -osd16  sdh3  135.1G  bluestore

    Separate Storage Groups

    DEPRECATED: Instead of manually needing to set this, the deviceClass property can be used on Pool structures in CephBlockPool, CephFilesystem and CephObjectStore CRD objects.

    By default Rook/Ceph puts all storage under one replication rule in the CRUSH Map which provides the maximum amount of storage capacity for a cluster. If you would like to use different storage endpoints for different purposes, you’ll have to create separate storage groups.

    In the following example we will separate SSD drives from spindle-based drives, a common practice for those looking to target certain workloads onto faster (database) or slower (file archive) storage.

    CRUSH Hierarchy

    To see the CRUSH hierarchy of all your hosts and OSDs run:

    ceph osd tree

    Before we separate our disks into groups, our example cluster looks like this:

    -1 7.21828 root default
    -2 0.94529     host node1
     0 0.55730         osd.0           up  1.00000          1.00000
     1 0.11020         osd.1           up  1.00000          1.00000
     2 0.27779         osd.2           up  1.00000          1.00000
    -3 1.22480     host node2
     3 0.55730         osd.3           up  1.00000          1.00000
     4 0.11020         osd.4           up  1.00000          1.00000
     5 0.55730         osd.5           up  1.00000          1.00000
    -4 1.22480     host node3
     6 0.55730         osd.6           up  1.00000          1.00000
     7 0.11020         osd.7           up  1.00000          1.00000
     8 0.06670         osd.8           up  1.00000          1.00000

    We have one root bucket default that every host and OSD is under, so all of these storage locations get pooled together for reads/writes/replication.

    Let’s say that osd.1, osd.3, and osd.7 are our small SSD drives that we want to use separately.

    First we will create a new root bucket called ssd in our CRUSH map. Under this new bucket we will add new host buckets for each node that contains an SSD drive so data can be replicated and used separately from the default HDD group.

    # Create a new tree in the CRUSH Map for SSD hosts and OSDs
    ceph osd crush add-bucket ssd root
    ceph osd crush add-bucket node1-ssd host
    ceph osd crush add-bucket node2-ssd host
    ceph osd crush add-bucket node3-ssd host
    ceph osd crush move node1-ssd root=ssd
    ceph osd crush move node2-ssd root=ssd
    ceph osd crush move node3-ssd root=ssd
    # Create a new rule for replication using the new tree
    ceph osd crush rule create-simple ssd ssd host firstn

    Secondly we will move the SSD OSDs into the new ssd tree, under their respective host buckets:

    ceph osd crush set osd.1 .1102 root=ssd host=node1-ssd
    ceph osd crush set osd.3 .1102 root=ssd host=node2-ssd
    ceph osd crush set osd.7 .1102 root=ssd host=node3-ssd

    It’s important to note that the ceph osd crush set command requires a weight to be specified (our example uses .1102). If you’d like to change their weight you can do that here, otherwise be sure to specify their original weight seen in the ceph osd tree output.

    So let’s look at our CRUSH tree again with these changes:

    -8 0.22040 root ssd
    -5 0.11020     host node1-ssd
     1 0.11020         osd.1           up  1.00000          1.00000
    -6 0.11020     host node2-ssd
     4 0.11020         osd.4           up  1.00000          1.00000
    -7 0.11020     host node3-ssd
     7 0.11020         osd.7           up  1.00000          1.00000
    -1 7.21828 root default
    -2 0.83509     host node1
     0 0.55730         osd.0           up  1.00000          1.00000
     2 0.27779         osd.2           up  1.00000          1.00000
    -3 1.11460     host node2
     3 0.55730         osd.3           up  1.00000          1.00000
     5 0.55730         osd.5           up  1.00000          1.00000
    -4 1.11460     host node3
     6 0.55730         osd.6           up  1.00000          1.00000
     8 0.55730         osd.8           up  1.00000          1.00000

    Using Disk Groups With Pools

    Now we have a separate storage group for our SSDs, but we can’t use that storage until we associate a pool with it. The default group already has a pool called rbd in many cases. If you created a pool via CustomResourceDefinition, it will use the default storage group as well.

    Here’s how to create new pools:

    # SSD backed pool with 128 (total) PGs
    ceph osd pool create ssd 128 128 replicated ssd

    Now all you need to do is create RBD images or Kubernetes StorageClasses that specify the ssd pool to put it to use.

    Configuring Pools

    Placement Group Sizing

    NOTE: Since Ceph Nautilus (v14.x), you can use the Ceph MGR pg_autoscaler module to auto scale the PGs as needed, for more information on this topic checkout Ceph New in Nautilus: PG merging and autotuning article.

    To enable the pg_autoscaler module automatically in a Rook Ceph cluster, you can comment in the pg_autoscaler entry in the spec.mgr.modules struct of CephCluster CRD.

    The general rules for deciding how many PGs your pool(s) should contain is:

    • Less than 5 OSDs set pg_num to 128
    • Between 5 and 10 OSDs set pg_num to 512
    • Between 10 and 50 OSDs set pg_num to 1024

    If you have more than 50 OSDs, you need to understand the tradeoffs and how to calculate the pg_num value by yourself. For calculating pg_num yourself please make use of the pgcalc tool.

    If you’re already using a pool it is generally safe to increase its PG count on-the-fly. Decreasing the PG count is not recommended on a pool that is in use. The safest way to decrease the PG count is to back-up the data, delete the pool, and recreate it. With backups you can try a few potentially unsafe tricks for live pools, documented here.

    Deleting A Pool

    Be warned that this deletes all data from the pool, so Ceph by default makes it somewhat difficult to do.

    First you must inject arguments to the Mon daemons to tell them to allow the deletion of pools. In Rook Tools you can do this:

    ceph tell mon.\* injectargs '--mon-allow-pool-delete=true'

    Then to delete a pool, rbd in this example, run:

    ceph osd pool rm rbd rbd --yes-i-really-really-mean-it

    Creating A Pool

    # Create a pool called rbd with 1024 total PGs, using the default
    # replication ruleset
    ceph osd pool create rbd 1024 1024 replicated replicated_ruleset

    replicated_ruleset is the default CRUSH rule that replicates between the hosts and OSDs in the default root hierarchy.

    Setting The Number Of Replicas

    The size setting of a pool tells the cluster how many copies of the data should be kept for redundancy. By default the cluster will distribute these copies between host buckets in the CRUSH Map This can be set when creating a pool via CustomResourceDefinition or after creation with ceph.

    So for example let’s change the size of the rbd pool to three:

    ceph osd pool set rbd size 3

    Now if you run ceph -s you may see “recovery” operations and PGs in “undersized” and other “unclean” states. The cluster is essentially fixing itself since the number of replicas has been increased, and should go back to “active/clean” state shortly, after data has been replicated between hosts. When that’s done you will be able to lose two of your storage nodes and still have access to all your data in that pool, since the CRUSH algorithm will guarantee that at least one replica will still be available on another storage node. Of course you will only have 1/3 the capacity as a tradeoff.

    Setting PG Count

    Be sure to read the placement group sizing section before changing the number of PGs.

    # Set the number of PGs in the rbd pool to 512
    ceph osd pool set rbd pg_num 512

    Custom ceph.conf Settings

    WARNING: The advised method for controlling Ceph configuration is to manually use the Ceph CLI or the Ceph dashboard because this offers the most flexibility. It is highly recommended that this only be used when absolutely necessary and that the config be reset to an empty string if/when the configurations are no longer necessary. Configurations in the config file will make the Ceph cluster less configurable from the CLI and dashboard and may make future tuning or debugging difficult.

    Setting configs via Ceph’s CLI requires that at least one mon be available for the configs to be set, and setting configs via dashboard requires at least one mgr to be available. Ceph may also have a small number of very advanced settings that aren’t able to be modified easily via CLI or dashboard. In order to set configurations before monitors are available or to set problematic configuration settings, the rook-config-override ConfigMap exists, and the config field can be set with the contents of a ceph.conf file. The contents will be propagated to all mon, mgr, OSD, MDS, and RGW daemons as an /etc/ceph/ceph.conf file.

    WARNING: Rook performs no validation on the config, so the validity of the settings is the user’s responsibility.

    If the rook-config-override ConfigMap is created before the cluster is started, the Ceph daemons will automatically pick up the settings. If you add the settings to the ConfigMap after the cluster has been initialized, each daemon will need to be restarted where you want the settings applied:

    • mons: ensure all three mons are online and healthy before restarting each mon pod, one at a time.
    • mgrs: the pods are stateless and can be restarted as needed, but note that this will disrupt the Ceph dashboard during restart.
    • OSDs: restart your the pods by deleting them, one at a time, and running ceph -s between each restart to ensure the cluster goes back to “active/clean” state.
    • RGW: the pods are stateless and can be restarted as needed.
    • MDS: the pods are stateless and can be restarted as needed.

    After the pod restart, the new settings should be in effect. Note that if the ConfigMap in the Ceph cluster’s namespace is created before the cluster is created, the daemons will pick up the settings at first launch.


    In this example we will set the default pool size to two, and tell OSD daemons not to change the weight of OSDs on startup.

    WARNING: Modify Ceph settings carefully. You are leaving the sandbox tested by Rook. Changing the settings could result in unhealthy daemons or even data loss if used incorrectly.

    When the Rook Operator creates a cluster, a placeholder ConfigMap is created that will allow you to override Ceph configuration settings. When the daemon pods are started, the settings specified in this ConfigMap will be merged with the default settings generated by Rook.

    The default override settings are blank. Cutting out the extraneous properties, we would see the following defaults after creating a cluster:

    $ kubectl -n rook-ceph get ConfigMap rook-config-override -o yaml
    kind: ConfigMap
    apiVersion: v1
      name: rook-config-override
      namespace: rook-ceph
      config: ""

    To apply your desired configuration, you will need to update this ConfigMap. The next time the daemon pod(s) start, they will use the updated configs.

    kubectl -n rook-ceph edit configmap rook-config-override

    Modify the settings and save. Each line you add should be indented from the config property as such:

    apiVersion: v1
    kind: ConfigMap
      name: rook-config-override
      namespace: rook-ceph
      config: |
        osd crush update on start = false
        osd pool default size = 2

    OSD CRUSH Settings

    A useful view of the CRUSH Map is generated with the following command:

    ceph osd tree

    In this section we will be tweaking some of the values seen in the output.

    OSD Weight

    The CRUSH weight controls the ratio of data that should be distributed to each OSD. This also means a higher or lower amount of disk I/O operations for an OSD with higher/lower weight, respectively.

    By default OSDs get a weight relative to their storage capacity, which maximizes overall cluster capacity by filling all drives at the same rate, even if drive sizes vary. This should work for most use-cases, but the following situations could warrant weight changes:

    • Your cluster has some relatively slow OSDs or nodes. Lowering their weight can reduce the impact of this bottleneck.
    • You’re using bluestore drives provisioned with Rook v0.3.1 or older. In this case you may notice OSD weights did not get set relative to their storage capacity. Changing the weight can fix this and maximize cluster capacity.

    This example sets the weight of osd.0 which is 600GiB

    ceph osd crush reweight osd.0 .600

    OSD Primary Affinity

    When pools are set with a size setting greater than one, data is replicated between nodes and OSDs. For every chunk of data a Primary OSD is selected to be used for reading that data to be sent to clients. You can control how likely it is for an OSD to become a Primary using the Primary Affinity setting. This is similar to the OSD weight setting, except it only affects reads on the storage device, not capacity or writes.

    In this example we will make sure osd.0 is only selected as Primary if all other OSDs holding replica data are unavailable:

    ceph osd primary-affinity osd.0 0

    OSD Dedicated Network

    It is possible to configure ceph to leverage a dedicated network for the OSDs to communicate across. A useful overview is the CEPH Networks section of the Ceph documentation. If you declare a cluster network, OSDs will route heartbeat, object replication and recovery traffic over the cluster network. This may improve performance compared to using a single network.

    Two changes are necessary to the configuration to enable this capability:

    Use hostNetwork in the rook ceph cluster configuration

    Enable the hostNetwork setting in the Ceph Cluster CRD configuration. For example,

        hostNetwork: true

    Define the subnets to use for public and private OSD networks

    Edit the rook-config-override configmap to define the custom network configuration:

    kubectl -n rook-ceph edit configmap rook-config-override

    In the editor, add a custom configuration to instruct ceph which subnet is the public network and which subnet is the private network. For example:

    apiVersion: v1
      config: |
        public network =
        cluster network =
        public addr = ""
        cluster addr = ""

    After applying the updated rook-config-override configmap, it will be necessary to restart the OSDs by deleting the OSD pods in order to apply the change. Restart the OSD pods by deleting them, one at a time, and running ceph -s between each restart to ensure the cluster goes back to “active/clean” state.

    Phantom OSD Removal

    If you have OSDs in which are not showing any disks, you can remove those “Phantom OSDs” by following the instructions below. To check for “Phantom OSDs”, you can run:

    ceph osd tree

    An example output looks like this:

     -1       57.38062 root default
    -13        7.17258     host node1.example.com
      2   hdd  3.61859         osd.2                up  1.00000 1.00000
     -7              0     host node2.example.com   down    0    1.00000

    The host node2.example.com in the output has no disks, so it is most likely a “Phantom OSD”.

    Now to remove it, use the ID in the first column of the output and replace <ID> with it. In the example output above the ID would be -7. The commands are:

    ceph osd out <ID>
    ceph osd crush remove osd.<ID>
    ceph auth del osd.<ID>
    ceph osd rm <ID>

    To recheck that the Phantom OSD got removed, re-run the following command and check if the OSD with the ID doesn’t show up anymore:

    ceph osd tree

    Change Failure Domain

    In Rook, it is now possible to indicate how the default CRUSH failure domain rule must be configured in order to ensure that replicas or erasure code shards are separated across hosts, and a single host failure does not affect availability. For instance, this is an example manifest of a block pool named replicapool configured with a failureDomain set to osd:

    apiVersion: ceph.rook.io/v1
    kind: CephBlockPool
      name: replicapool
      namespace: rook
      # The failure domain will spread the replicas of the data across different failure zones
      failureDomain: osd

    However, due to several reasons, we may need to change such failure domain to its other value: host. Unfortunately, changing it directly in the YAML manifest is not currently handled by Rook, so we need to perform the change directly using Ceph commands using the Rook tools pod, for instance:

    $ ceph osd pool get replicapool crush_rule
    crush_rule: replicapool
    $ceph osd crush rule create-replicated replicapool_host_rule default host

    Notice that the suffix host_rule in the name of the rule is just for clearness about the type of rule we are creating here, and can be anything else as long as it is different from the existing one. Once the new rule has been created, we simply apply it to our block pool:

    ceph osd pool set replicapool crush_rule replicapool_host_rule

    And validate that it has been actually applied properly:

    $ ceph osd pool get replicapool crush_rule
    crush_rule: replicapool_host_rule

    If the cluster’s health was HEALTH_OK when we performed this change, immediately, the new rule is applied to the cluster transparently without service disruption.

    Exactly the same approach can be used to change from host back to osd.

    Monitor placement

    Rook will try to schedule Ceph monitor pods on different physical nodes by default. When available, Rook will also consider failure domain information in the form of Kubernetes node labels when scheduling Ceph monitors.

    Currently Rook supports the node label topology.kubernetes.io/zone=<zone> which can be applied to a node to specify its failure domain using the command:

    kubectl label node <node> topology.kubernetes.io/zone=<zone>

    For versions previous to K8s 1.17, use the topology key: failure-domain.beta.kubernetes.io/zone

    Rook uses failure domain labels by trying to schedule monitor pods on different failure domains. And all nodes without failure domain labels are treated as a single failure domain from a scheduling point of view. When placing multiple monitor pods within a single failure domain Rook will try to run the pods on different physical nodes.