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Ceph 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.

Using alternate namespaces

If you wish to deploy the Rook Operator and/or Ceph clusters to namespaces other than the default rook-ceph, the manifests are commented to allow for easy sed replacements. Change ROOK_CLUSTER_NAMESPACE to tailor the manifests for additional Ceph clusters. You can choose to also change ROOK_OPERATOR_NAMESPACE to create a new Rook Operator for each Ceph cluster (don't forget to set ROOK_CURRENT_NAMESPACE_ONLY), or you can leave it at the same value for every Ceph cluster if you only wish to have one Operator manage all Ceph clusters.

If the operator namespace is different from the cluster namespace, the operator namespace must be created before running the steps below. The cluster namespace does not need to be created first, as it will be created by common.yaml in the script below.

kubectl create namespace $ROOK_OPERATOR_NAMESPACE

This will help you manage namespaces more easily, but you should still make sure the resources are configured to your liking.

cd deploy/examples

export ROOK_OPERATOR_NAMESPACE="rook-ceph"
export ROOK_CLUSTER_NAMESPACE="rook-ceph"

sed -i.bak \
    -e "s/\(.*\):.*# namespace:operator/\1: $ROOK_OPERATOR_NAMESPACE # namespace:operator/g" \
    -e "s/\(.*\):.*# namespace:cluster/\1: $ROOK_CLUSTER_NAMESPACE # namespace:cluster/g" \
    -e "s/\(.*serviceaccount\):.*:\(.*\) # serviceaccount:namespace:operator/\1:$ROOK_OPERATOR_NAMESPACE:\2 # serviceaccount:namespace:operator/g" \
    -e "s/\(.*serviceaccount\):.*:\(.*\) # serviceaccount:namespace:cluster/\1:$ROOK_CLUSTER_NAMESPACE:\2 # serviceaccount:namespace:cluster/g" \
    -e "s/\(.*\): [-_A-Za-z0-9]*\.\(.*\) # driver:namespace:cluster/\1: $ROOK_CLUSTER_NAMESPACE.\2 # driver:namespace:cluster/g" \
  common.yaml operator.yaml cluster.yaml # add other files or change these as desired for your config

# You need to use `apply` for all Ceph clusters after the first if you have only one Operator
kubectl apply -f common.yaml -f operator.yaml -f cluster.yaml # add other files as desired for yourconfig

Also see the CSI driver documentation to update the csi provisioner names in the storageclass and volumesnapshotclass.

Deploying a second cluster

If you wish to create a new CephCluster in a separate namespace, you can easily do so by modifying the ROOK_OPERATOR_NAMESPACE and SECOND_ROOK_CLUSTER_NAMESPACE values in the below instructions. The default configuration in common-second-cluster.yaml is already set up to utilize rook-ceph for the operator and rook-ceph-secondary for the cluster. There's no need to run the sed command if you prefer to use these default values.

cd deploy/examples
export ROOK_OPERATOR_NAMESPACE="rook-ceph"
export SECOND_ROOK_CLUSTER_NAMESPACE="rook-ceph-secondary"

sed -i.bak \
    -e "s/\(.*\):.*# namespace:operator/\1: $ROOK_OPERATOR_NAMESPACE # namespace:operator/g" \
    -e "s/\(.*\):.*# namespace:cluster/\1: $SECOND_ROOK_CLUSTER_NAMESPACE # namespace:cluster/g" \

kubectl create -f common-second-cluster.yaml

This will create all the necessary RBACs as well as the new namespace. The script assumes that common.yaml was already created. When you create the second CephCluster CR, use the same NAMESPACE and the operator will configure the second cluster.

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[*]}')
    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}"

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 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[*]}')

# 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/ceph/osd/ceph-*; 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.

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


It is deprecated to manually need 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.

Configuring Pools

Placement Group Sizing


Since Ceph Nautilus (v14.x), you can use the Ceph MGR pg_autoscaler module to auto scale the PGs as needed. It is highly advisable to configure default pg_num value on per-pool basis, If you want to enable this feature, please refer to Default PG and PGP counts.

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

  • Fewer 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.

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


The advised method for controlling Ceph configuration is to use the cephConfig: structure in the CephCluster CRD.

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 also has a number of very advanced settings that cannot be modified easily via the CLI or dashboard. In order to set configurations before monitors are available or to set advanced 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.


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.

To automate the restart of the Ceph daemon pods, you will need to trigger an update to the pod specs. The simplest way to trigger the update is to add annotations or labels to the CephCluster CR for the daemons you want to restart. The operator will then proceed with a rolling update, similar to any other update to the cluster.


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.


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

Custom CSI ceph.conf Settings


It is highly recommended to use the default setting that comes with CephCSI and this can only be used when absolutely necessary. The ceph.conf should be reset back to default values if/when the configurations are no longer necessary.

If the csi-ceph-conf-override ConfigMap is created before the cluster is started, the CephCSI pods will automatically pick up the settings. If you add the settings to the ConfigMap after the cluster has been initialized, you can restart the Rook operator pod and wait for Rook to recreate CSI pods to take immediate effect.

After the CSI pods are restarted, the new settings should be in effect.

Example CSI ceph.conf Settings

In this Example we will set the rbd_validate_pool to false to skip rbd pool validation.


Modify Ceph settings carefully to avoid modifying the default configuration. Changing the settings could result in unexpected results if used incorrectly.

kubectl create -f csi-ceph-conf-override.yaml

Restart the Rook operator pod and wait for CSI pods to be recreated.

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 ensure that osd.0 is only selected as Primary if all other OSDs holding data replicas are unavailable:

ceph osd primary-affinity osd.0 0

OSD Dedicated Network


This documentation is left for historical purposes. It is still valid, but Rook offers native support for this feature via the CephCluster network configuration.

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, especially when slower network technologies are used. The tradeoff is additional expense and subtle failure modes.

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

Use hostNetwork in the cluster configuration

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

    provider: host


Changing this setting is not supported in a running Rook cluster. Host networking should be configured when the cluster is first created.

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 (example output):

$ ceph osd tree
-1       57.38062 root default
-13        7.17258     host
2   hdd  3.61859         osd.2                up  1.00000 1.00000
-7              0     host   down    0    1.00000

The host 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 was removed, re-run the following command and check if the OSD with the ID doesn't show up anymore:

ceph osd tree

Auto Expansion of OSDs

Prerequisites for Auto Expansion of OSDs

1) A PVC-based cluster deployed in dynamic provisioning environment with a storageClassDeviceSet.

2) Create the Rook Toolbox.


Prometheus Operator and [Prometheus ../Monitoring/ are Prerequisites that are created by the auto-grow-storage script.

To scale OSDs Vertically

Run the following script to auto-grow the size of OSDs on a PVC-based Rook cluster whenever the OSDs have reached the storage near-full threshold.

tests/scripts/ size  --max maxSize --growth-rate percent

growth-rate percentage represents the percent increase you want in the OSD capacity and maxSize represent the maximum disk size.

For example, if you need to increase the size of OSD by 30% and max disk size is 1Ti

./ size  --max 1Ti --growth-rate 30

To scale OSDs Horizontally

Run the following script to auto-grow the number of OSDs on a PVC-based Rook cluster whenever the OSDs have reached the storage near-full threshold.

tests/scripts/ count --max maxCount --count rate

Count of OSD represents the number of OSDs you need to add and maxCount represents the number of disks a storage cluster will support.

For example, if you need to increase the number of OSDs by 3 and maxCount is 10

./ count --max 10 --count 3