7 Ceph cluster custom resource definitions #

If these settings are changed in the CRD, the operator will update the number of MONs during a periodic check of the MON health, which by default is every 45 seconds.

To change the defaults that the operator uses to determine the MON health and whether to failover a MON, refer to the Section 7.1.3.15, “Health settings”. The intervals should be small enough that you have confidence the MONs will maintain quorum, while also being long enough to ignore network blips where MONs are failed over too often.

You can use the cluster CR to enable or disable any manager module. For example, this can be configured:

mgr:
  modules:
  - name: <name of the module>
    enabled: true

Some modules will have special configuration to ensure the module is fully functional after being enabled. Specifically, the pg_autoscaler—Rook will configure all new pools with PG autoscaling by setting: osd_pool_default_pg_autoscale_mode = on

If not specified, the default SDN will be used. Configure the network that will be enabled for the cluster and services.

Note

Changing networking configuration after a Ceph cluster has been deployed is not supported and will result in a non-functioning cluster.

To use host networking, set provider: host.

In addition to the cluster level settings specified above, each individual node can also specify configuration to override the cluster level settings and defaults. If a node does not specify any configuration, then it will inherit the cluster level settings.

When useAllNodes is set to true, Rook attempts to make Ceph cluster management as hands-off as possible while still maintaining reasonable data safety. If a usable node comes online, Rook will begin to use it automatically. To maintain a balance between hands-off usability and data safety, nodes are removed from Ceph as OSD hosts only (1) if the node is deleted from Kubernetes itself or (2) if the node has its taints or affinities modified in such a way that the node is no longer usable by Rook. Any changes to taints or affinities, intentional or unintentional, may affect the data reliability of the Ceph cluster. In order to help protect against this somewhat, deletion of nodes by taint or affinity modifications must be confirmed by deleting the Rook-Ceph operator pod and allowing the operator deployment to restart the pod.

For production clusters, we recommend that useAllNodes is set to false to prevent the Ceph cluster from suffering reduced data reliability unintentionally due to a user mistake. When useAllNodes is set to false, Rook relies on the user to be explicit about when nodes are added to or removed from the Ceph cluster. Nodes are only added to the Ceph cluster if the node is added to the Ceph cluster resource. Similarly, nodes are only removed if the node is removed from the Ceph cluster resource.

kubectl -n rook-ceph edit cephcluster rook-ceph

Below are the settings available, both at the cluster and individual node level, for selecting which storage resources will be included in the cluster.

The following are the settings for Storage Class Device Sets which can be configured to create OSDs that are backed by block mode PVs.

Ceph DriveGroups allow for specifying highly advanced OSD layouts. Refer to Seção 13.4.3, “Adicionando OSDs por meio da especificação DriveGroups” for both general information and detailed specification of DriveGroups with useful examples.

Important

When managing a Rook/Ceph cluster’s OSD layouts with DriveGroups, the storage configuration is mostly ignored. storageClassDeviceSets can still be used to create OSDs on PVC, but Rook will no longer use storage configurations for creating OSDs on a node's devices. To avoid confusion, we recommend using the storage configuration or DriveGroups, but never both. Because storage and DriveGroups should not be used simultaneously, Rook only supports provisioning OSDs with DriveGroups on new Rook-Ceph clusters.

DriveGroups are defined by a name, a Ceph DriveGroups spec, and a Rook placement.

Annotations and Labels can be specified so that the Rook components will have those annotations or labels added to them.

You can set annotations and labels for Rook components for the list of key value pairs:

When other keys are set, all will be merged together with the specific component.

Placement configuration for the cluster services. It includes the following keys: mgr, mon, osd, cleanup, and all. Each service will have its placement configuration generated by merging the generic configuration under all with the most specific one (which will override any attributes).

Note

Placement of OSD pods is controlled using the Section 7.1.3.8, “Storage class device sets”, not the general placement configuration.

A placement configuration is specified (according to the Kubernetes PodSpec) as:

If you use labelSelector for OSD pods, you must write two rules both for rook-ceph-osd and rook-ceph-osd-prepare.

The Rook Ceph operator creates a job called rook-ceph-detect-version to detect the full Ceph version used by the given cephVersion.image. The placement from the MON section is used for the job except for the PodAntiAffinity field.

Resources should be specified so that the Rook components are handled after Kubernetes Pod Quality of Service classes. This allows to keep Rook components running when for example a node runs out of memory and the Rook components are not killed depending on their Quality of Service class.

You can set resource requests/limits for Rook components through the Section 7.1.3.13, “Resource requirements and limits” structure in the following keys:

In order to provide the best possible experience running Ceph in containers, Rook internally recommends minimum memory limits if resource limits are passed. If a user configures a limit or request value that is too low, Rook will still run the pod(s) and print a warning to the operator log.

Priority class names can be specified so that the Rook components will have those priority class names added to them.

You can set priority class names for Rook components for the list of key value pairs:

The specific component keys will act as overrides to all.

Rook-Ceph will monitor the state of the CephCluster on various components by default. The following CRD settings are available:

Currently three health checks are implemented:

The liveness probe of each daemon can also be controlled via livenessProbe. The setting is valid for mon, mgr and osd. Here is a complete example for both daemonHealth and livenessProbe:

healthCheck:
  daemonHealth:
    mon:
      disabled: false
      interval: 45s
      timeout: 600s
    osd:
      disabled: false
      interval: 60s
    status:
      disabled: false
  livenessProbe:
    mon:
      disabled: false
    mgr:
      disabled: false
    osd:
      disabled: false

You can change the mgr probe by applying the following:

healthCheck:
  livenessProbe:
    mgr:
      disabled: false
      probe:
        httpGet:
          path: /
          port: 9283
        initialDelaySeconds: 3
        periodSeconds: 3

Changing the liveness probe is an advanced operation and should rarely be necessary. If you want to change these settings, start with the probe specification that Rook generates by default and then modify the desired settings.

Individual nodes and their configurations can be specified so that only the named nodes below will be used as storage resources. Each node’s “name” field should match their “kubernetes.io/hostname” label.

apiVersion: ceph.rook.io/v1
kind: CephCluster
metadata:
  name: rook-ceph
  namespace: rook-ceph
spec:
  cephVersion:
    image: ceph/ceph:v15.2.4
  dataDirHostPath: /var/lib/rook
  mon:
    count: 3
    allowMultiplePerNode: true
  dashboard:
    enabled: true
  # cluster level storage configuration and selection
  storage:
    useAllNodes: false
    useAllDevices: false
    deviceFilter:
    config:
      metadataDevice:
      databaseSizeMB: "1024" # this value can be removed for environments with normal sized disks (100 GB or larger)
    nodes:
    - name: "172.17.4.201"
      devices:             # specific devices to use for storage can be specified for each node
      - name: "sdb" # Whole storage device
      - name: "sdc1" # One specific partition. Should not have a file system on it.
      - name: "/dev/disk/by-id/ata-ST4000DM004-XXXX" # both device name and explicit udev links are supported
      config:         # configuration can be specified at the node level which overrides the cluster level config
        storeType: bluestore
    - name: "172.17.4.301"
      deviceFilter: "^sd."

To control where various services will be scheduled by Kubernetes, use the placement configuration sections below. The example under “all” would have all services scheduled on Kubernetes nodes labeled with “role=storage-node” and tolerate taints with a key of “storage-node”.

apiVersion: ceph.rook.io/v1
kind: CephCluster
metadata:
  name: rook-ceph
  namespace: rook-ceph
spec:
  cephVersion:
    image: ceph/ceph:v15.2.4
  dataDirHostPath: /var/lib/rook
  mon:
    count: 3
    allowMultiplePerNode: true
  # enable the Ceph dashboard for viewing cluster status
  dashboard:
    enabled: true
  placement:
    all:
      nodeAffinity:
        requiredDuringSchedulingIgnoredDuringExecution:
          nodeSelectorTerms:
          - matchExpressions:
            - key: role
              operator: In
              values:
              - storage-node
      tolerations:
      - key: storage-node
        operator: Exists
    mgr:
      nodeAffinity:
      tolerations:
    mon:
      nodeAffinity:
      tolerations:
    osd:
      nodeAffinity:
      tolerations:

To control how many resources the Rook components can request/use, you can set requests and limits in Kubernetes for them. You can override these requests and limits for OSDs per node when using useAllNodes: false in the node item in the nodes list.

Warning

Before setting resource requests/limits, review the Ceph documentation for hardware recommendations for each component.

apiVersion: ceph.rook.io/v1
kind: CephCluster
metadata:
  name: rook-ceph
  namespace: rook-ceph
spec:
  cephVersion:
    image: ceph/ceph:v15.2.4
  dataDirHostPath: /var/lib/rook
  mon:
    count: 3
    allowMultiplePerNode: true
  # enable the Ceph dashboard for viewing cluster status
  dashboard:
    enabled: true
  # cluster level resource requests/limits configuration
  resources:
  storage:
    useAllNodes: false
    nodes:
    - name: "172.17.4.201"
      resources:
        limits:
          cpu: "2"
          memory: "4096Mi"
        requests:
          cpu: "2"
          memory: "4096Mi"

The topology of the cluster is important in production environments where you want your data spread across failure domains. The topology can be controlled by adding labels to the nodes. When the labels are found on a node at first OSD deployment, Rook will add them to the desired level in the CRUSH map.

The complete list of labels in hierarchy order from highest to lowest is:

topology.kubernetes.io/region
topology.kubernetes.io/zone
topology.rook.io/datacenter
topology.rook.io/room
topology.rook.io/pod
topology.rook.io/pdu
topology.rook.io/row
topology.rook.io/rack
topology.rook.io/chassis

For example, if the following labels were added to a node:

kubectl label node mynode topology.kubernetes.io/zone=zone1
kubectl label node mynode topology.rook.io/rack=rack1

Note

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

These labels would result in the following hierarchy for OSDs on that node (this command can be run in the Rook toolbox):

[root@mynode /]# ceph osd tree
ID CLASS WEIGHT  TYPE NAME                 STATUS REWEIGHT PRI-AFF
-1       0.01358 root default
-5       0.01358     zone zone1
-4       0.01358         rack rack1
-3       0.01358             host mynode
 0   hdd 0.00679                 osd.0         up  1.00000 1.00000
 1   hdd 0.00679                 osd.1         up  1.00000 1.00000

Ceph requires unique names at every level in the hierarchy (CRUSH map). For example, you cannot have two racks with the same name that are in different zones. Racks in different zones must be named uniquely.

Note that the host is added automatically to the hierarchy by Rook. The host cannot be specified with a topology label. All topology labels are optional.

Tip

When setting the node labels prior to CephCluster creation, these settings take immediate effect. However, applying this to an already deployed CephCluster requires removing each node from the cluster first and then re-adding it with new configuration to take effect. Do this node by node to keep your data safe! Check the result with ceph osd tree from the Chapter 9, Toolboxes. The OSD tree should display the hierarchy for the nodes that already have been re-added.

To utilize the failureDomain based on the node labels, specify the corresponding option in the CephBlockPool.

apiVersion: ceph.rook.io/v1
kind: CephBlockPool
metadata:
  name: replicapool
  namespace: rook-ceph
spec:
  failureDomain: rack  # this matches the topology labels on nodes
  replicated:
    size: 3

This configuration will split the replication of volumes across unique racks in the data center setup.

In the CRD specification below three monitors are created each using a 10Gi PVC created by Rook using the local-storage storage class.

apiVersion: ceph.rook.io/v1
kind: CephCluster
metadata:
  name: rook-ceph
  namespace: rook-ceph
spec:
  cephVersion:
    image: ceph/ceph:v15.2.4
  dataDirHostPath: /var/lib/rook
  mon:
    count: 3
    allowMultiplePerNode: false
    volumeClaimTemplate:
      spec:
        storageClassName: local-storage
        resources:
          requests:
            storage: 10Gi
  dashboard:
    enabled: true
  storage:
    useAllNodes: true
    useAllDevices: true
    deviceFilter:
    config:
      metadataDevice:
      databaseSizeMB: "1024" # this value can be removed for environments with normal sized disks (100 GB or larger)
      journalSizeMB: "1024"  # this value can be removed for environments with normal sized disks (20 GB or larger)
      osdsPerDevice: "1"

In the CRD specification below, three OSDs (having specific placement and resource values) and three MONs with each using a 10Gi PVC, are created by Rook using the local-storage storage class.

apiVersion: ceph.rook.io/v1
kind: CephCluster
metadata:
  name: rook-ceph
  namespace: rook-ceph
spec:
  dataDirHostPath: /var/lib/rook
  mon:
    count: 3
    allowMultiplePerNode: false
    volumeClaimTemplate:
      spec:
        storageClassName: local-storage
        resources:
          requests:
            storage: 10Gi
  cephVersion:
    image: ceph/ceph:v15.2.4
    allowUnsupported: false
  dashboard:
    enabled: true
  network:
    hostNetwork: false
  storage:
    storageClassDeviceSets:
    - name: set1
      count: 3
      portable: false
      tuneDeviceClass: false
      resources:
        limits:
          cpu: "500m"
          memory: "4Gi"
        requests:
          cpu: "500m"
          memory: "4Gi"
      placement:
        podAntiAffinity:
          preferredDuringSchedulingIgnoredDuringExecution:
          - weight: 100
            podAffinityTerm:
              labelSelector:
                matchExpressions:
                - key: "rook.io/cluster"
                  operator: In
                  values:
                    - cluster1
                topologyKey: "topology.kubernetes.io/zone"
      volumeClaimTemplates:
      - metadata:
          name: data
        spec:
          resources:
            requests:
              storage: 10Gi
          storageClassName: local-storage
          volumeMode: Block
          accessModes:
            - ReadWriteOnce

In the simplest case, Ceph OSD BlueStore consumes a single (primary) storage device. BlueStore is the engine used by the OSD to store data.

The storage device is normally used as a whole, occupying the full device that is managed directly by BlueStore. It is also possible to deploy BlueStore across additional devices such as a DB device. This device can be used for storing BlueStore’s internal metadata. BlueStore (or rather, the embedded RocksDB) will put as much metadata as it can on the DB device to improve performance. If the DB device fills up, metadata will spill back onto the primary device (where it would have been otherwise). Again, it is only helpful to provision a DB device if it is faster than the primary device.

You can have multiple volumeClaimTemplates where each might either represent a device or a metadata device. So just taking the storage section this will give something like:

  storage:
   storageClassDeviceSets:
    - name: set1
      count: 3
      portable: false
      tuneDeviceClass: false
      volumeClaimTemplates:
      - metadata:
          name: data
        spec:
          resources:
            requests:
              storage: 10Gi
          # IMPORTANT: Change the storage class depending on your environment (e.g. local-storage, gp2)
          storageClassName: gp2
          volumeMode: Block
          accessModes:
            - ReadWriteOnce
      - metadata:
          name: metadata
        spec:
          resources:
            requests:
              # Find the right size https://docs.ceph.com/docs/master/rados/configuration/bluestore-config-ref/#sizing
              storage: 5Gi
          # IMPORTANT: Change the storage class depending on your environment (e.g. local-storage, io1)
          storageClassName: io1
          volumeMode: Block
          accessModes:
            - ReadWriteOnce

Note

Rook only supports three naming conventions for a given template:

• data: represents the main OSD block device, where your data is being stored.

• metadata: represents the metadata (including block.db and block.wal) device used to store the Ceph Bluestore database for an OSD.

• “wal”: represents the block.wal device used to store the Ceph BlueStore database for an OSD. If this device is set, “metadata” device will refer specifically to the block.db device. It is recommended to use a faster storage class for the metadata or wal device, with a slower device for the data. Otherwise, having a separate metadata device will not improve the performance.

The BlueStore partition has the following reference combinations supported by the ceph-volume utility:

With the present configuration, each OSD will have its main block allocated a 10 GB device as well a 5 GB device to act as a BlueStore database.

The minimum supported Ceph version for the External Cluster is Luminous 12.2.x.

The features available from the external cluster will vary depending on the version of Ceph. The following table shows the minimum version of Ceph for some of the features:

7.1.4.9.1 Prerequisites #

 

In order to configure an external Ceph cluster with Rook, we need to inject some information in order to connect to that cluster. You can use the cluster/examples/kubernetes/ceph/import-external-cluster.sh script to achieve that. The script will look for the following populated environment variables:

• NAMESPACE: the namespace where the configmap and secrets should be injected

• ROOK_EXTERNAL_FSID: the FSID of the external Ceph cluster. This can be retrieved via the ceph fsid command.

• ROOK_EXTERNAL_CEPH_MON_DATA: this is a comma- separated list of running monitors' IP addresses along with their ports. For example, a=172.17.0.4:6789,b=172.17.0.5:6789,c=172.17.0.6:6789. You do not need to specify all the monitors; you can simply pass one, and the operator will discover the rest. The name of the monitor is the name that appears in the ceph status output.

Now, we need to give Rook a key to connect to the cluster in order to perform various operations, such as cluster health checks, CSI keys management, etc. We recommend generating keys with minimal access, so the admin key does not need to be used by the external cluster. In this case, the admin key is only needed to generate the keys that will be used by the external cluster. If the admin key is to be used by the external cluster, however, set the following variable:

• ROOK_EXTERNAL_ADMIN_SECRET: OPTIONAL: the external Ceph cluster admin secret key. This can be retrieved via the ceph auth get-key client.admin command.

Note

WARNING: If you plan to create CRs (pool, rgw, mds, nfs) in the external cluster, you MUST inject the client.admin keyring as well as injecting cluster-external-management.yaml

Example:

export NAMESPACE=rook-ceph-external
export ROOK_EXTERNAL_FSID=3240b4aa-ddbc-42ee-98ba-4ea7b2a61514
export ROOK_EXTERNAL_CEPH_MON_DATA=a=172.17.0.4:6789
export ROOK_EXTERNAL_ADMIN_SECRET=AQC6Ylxdja+NDBAAB7qy9MEAr4VLLq4dCIvxtg==

If the Ceph admin key is not provided, the following script needs to be executed on a machine that can connect to the Ceph cluster using the Ceph admin key. On that machine, run cluster/examples/kubernetes/ceph/create-external-cluster-resources.sh. The script will automatically create users and keys with the lowest possible privileges and populate the necessary environment variables for cluster/examples/kubernetes/ceph/import-external-cluster.sh to work correctly.

Finally, execute the script like this from a machine that has access to your Kubernetes cluster:

bash cluster/examples/kubernetes/ceph/import-external-cluster.sh

7.1.4.9.2 CephCluster example (consumer) #

 

Assuming the above section has successfully completed, here is a CR example:

apiVersion: ceph.rook.io/v1
kind: CephCluster
metadata:
  name: rook-ceph-external
  namespace: rook-ceph-external
spec:
  external:
    enable: true
  crashCollector:
    disable: true
  # optionally, the ceph-mgr IP address can be pass to gather metric from the prometheus exporter
  #monitoring:
    #enabled: true
    #rulesNamespace: rook-ceph
    #externalMgrEndpoints:
      #- ip: 192.168.39.182

Choose the namespace carefully; if you have an existing cluster managed by Rook, you have likely already injected common.yaml. Additionally, you need to inject common-external.yaml too.

You can now create it like this:

kubectl create -f cluster/examples/kubernetes/ceph/cluster-external.yaml

If the previous section has not been completed, the Rook Operator will still acknowledge the CR creation but will wait forever to receive connection information.

Warning

If no cluster is managed by the current Rook Operator, you need to inject common.yaml, then modify cluster-external.yaml and specify rook-ceph as namespace.

If this is successful, you will see the CephCluster status as connected.

kubectl get CephCluster -n rook-ceph-external
NAME                 DATADIRHOSTPATH   MONCOUNT   AGE    STATE       HEALTH
rook-ceph-external   /var/lib/rook                162m   Connected   HEALTH_OK

Before you create a StorageClass with this cluster you will need to create a pool in your external Ceph Cluster.

rados df
POOL_NAME     USED OBJECTS CLONES COPIES MISSING_ON_PRIMARY UNFOUND DEGRADED RD_OPS  RD WR_OPS  WR USED COMPR UNDER COMPR
replicated_2g  0 B       0      0      0                  0       0        0      0 0 B      0 0 B        0 B         0 B

cat << EOF | kubectl apply -f -
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
   name: rook-ceph-block-ext
# Change "rook-ceph" provisioner prefix to match the operator namespace if needed
provisioner: rook-ceph.rbd.csi.ceph.com
parameters:
    # clusterID is the namespace where the rook cluster is running
    clusterID: rook-ceph-external
    # Ceph pool into which the RBD image shall be created
    pool: replicated_2g

    # RBD image format. Defaults to "2".
    imageFormat: "2"

    # RBD image features. Available for imageFormat: "2". CSI RBD currently supports only `layering` feature.
    imageFeatures: layering

    # The secrets contain Ceph admin credentials.
    csi.storage.k8s.io/provisioner-secret-name: rook-csi-rbd-provisioner
    csi.storage.k8s.io/provisioner-secret-namespace: rook-ceph-external
    csi.storage.k8s.io/controller-expand-secret-name: rook-csi-rbd-provisioner
    csi.storage.k8s.io/controller-expand-secret-namespace: rook-ceph-external
    csi.storage.k8s.io/node-stage-secret-name: rook-csi-rbd-node
    csi.storage.k8s.io/node-stage-secret-namespace: rook-ceph-external

    # Specify the filesystem type of the volume. If not specified, csi-provisioner
    # will set default as `ext4`. Note that `xfs` is not recommended due to potential deadlock
    # in hyperconverged settings where the volume is mounted on the same node as the osds.
    csi.storage.k8s.io/fstype: ext4

# Delete the rbd volume when a PVC is deleted
reclaimPolicy: Delete
allowVolumeExpansion: true
EOF

apiVersion: ceph.rook.io/v1
kind: CephCluster
metadata:
  name: rook-ceph-external
  namespace: rook-ceph-external
spec:
  external:
    enable: true
  dataDirHostPath: /var/lib/rook
  cephVersion:
    image: ceph/ceph:v15.2.4 # Should match external cluster version

Rook has the ability to cleanup resources and data that were deployed when a delete cephcluster command is issued. The policy represents the confirmation that cluster data should be forcibly deleted. The cleanupPolicy should only be added to the cluster when the cluster is about to be deleted. After the confirmation field of the cleanup policy is set, Rook will stop configuring the cluster as if the cluster is about to be destroyed in order to prevent these settings from being deployed unintentionally. The cleanupPolicy CR settings has different fields:

To automate activation of the cleanup, you can use the following command:

Warning

Data will be permanently deleted.

kubectl -n rook-ceph patch cephcluster rook-ceph --type merge \
 -p '{"spec":{"cleanupPolicy":{"confirmation":"yes-really-destroy-data"}}}'

Nothing will happen until the deletion of the CR is requested, so this can still be reverted. However, all new configuration by the operator will be blocked with this cleanup policy enabled.

Rook waits for the deletion of PVs provisioned using the CephCluster before proceeding to delete the CephCluster. To force deletion of the CephCluster without waiting for the PVs to be deleted, you can set the allowUninstallWithVolumes to true under spec.CleanupPolicy.

For optimal performance, while also adding redundancy, this sample will configure Ceph to make three full copies of the data on multiple nodes.

Note

This sample requires at least one OSD per node, with each OSD located on three different nodes.

Each OSD must be located on a different node, because the failureDomain is set to host and the replicated.size is set to three.

apiVersion: ceph.rook.io/v1
kind: CephBlockPool
metadata:
  name: replicapool
  namespace: rook-ceph
spec:
  failureDomain: host
  replicated:
    size: 3
  deviceClass: hdd

This sample will lower the overall storage capacity requirement, while also adding redundancy by using Section 7.2.2.4, “Erasure coding”.

Note

This sample requires at least three BlueStore OSDs.

The OSDs can be located on a single Ceph node or spread across multiple nodes, because the failureDomain is set to osd and the erasureCoded chunk settings require at least three different OSDs (two dataChunks + one codingChunks).

apiVersion: ceph.rook.io/v1
kind: CephBlockPool
metadata:
  name: ecpool
  namespace: rook-ceph
spec:
  failureDomain: osd
  erasureCoded:
    dataChunks: 2
    codingChunks: 1
  deviceClass: hdd

High performance applications typically will not use erasure coding due to the performance overhead of creating and distributing the chunks in the cluster.

When creating an erasure-coded pool, we recommend creating the pool when you have BlueStore OSDs in your cluster.

With poolProperties you can set any pool property:

spec:
  parameters:
    <name of the parameter>: <parameter value>

For example:

spec:
  parameters:
    min_size: 1

Erasure coding allows you to keep your data safe while reducing the storage overhead. Instead of creating multiple replicas of the data, erasure coding divides the original data into chunks of equal size, then generates extra chunks of that same size for redundancy.

For example, if you have an object of size 2 MB, the simplest erasure coding with two data chunks would divide the object into two chunks of size 1 MB each (data chunks). One more chunk (coding chunk) of size 1 MB will be generated. In total, 3 MB will be stored in the cluster. The object will be able to suffer the loss of any one of the chunks and still be able to reconstruct the original object.

The number of data and coding chunks you choose will depend on your resiliency to loss and how much storage overhead is acceptable in your storage cluster. Here are some examples to illustrate how the number of chunks affects the storage and loss toleration.

The failureDomain must be also be taken into account when determining the number of chunks. The failure domain determines the level in the Ceph CRUSH hierarchy where the chunks must be uniquely distributed. This decision will impact whether node losses or disk losses are tolerated. There could also be performance differences of placing the data across nodes or OSDs.

If you do not have a sufficient number of hosts or OSDs for unique placement the pool can be created, writing to the pool will hang.

Rook currently only configures two levels in the CRUSH map. It is also possible to configure other levels such as rack with by adding topology labels to the nodes.

Note

This sample requires at least one OSD per node, with each OSD located on three different nodes.

Each OSD must be located on a different node, because both of the defined pools set the failureDomain to host and the replicated.size to three.

The failureDomain can also be set to another location type (for example, rack), if it has been added as a location in the Storage Selection Settings.

  apiVersion: ceph.rook.io/v1
  kind: CephFilesystem
  metadata:
    name: myfs
    namespace: rook-ceph
  spec:
    metadataPool:
      failureDomain: host
      replicated:
        size: 3
    dataPools:
      - failureDomain: host
        replicated:
          size: 3
    preservePoolsOnDelete: true
    metadataServer:
      activeCount: 1
      activeStandby: true
      # A key/value list of annotations
      annotations:
      #  key: value
      placement:
      #  nodeAffinity:
      #    requiredDuringSchedulingIgnoredDuringExecution:
      #      nodeSelectorTerms:
      #      - matchExpressions:
      #        - key: role
      #          operator: In
      #          values:
      #          - mds-node
      #  tolerations:
      #  - key: mds-node
      #    operator: Exists
      #  podAffinity:
      #  podAntiAffinity:
      #  topologySpreadConstraints:
      resources:
      #  limits:
      #    cpu: "500m"
      #    memory: "1024Mi"
      #  requests:
      #    cpu: "500m"
      #    memory: "1024Mi"

These definitions can be found in the filesystem.yaml file.

Erasure coded pools require the OSDs to use BlueStore for the configured storeType. Additionally, erasure coded pools can only be used with dataPools. The metadataPool must use a replicated pool.

Note

This sample requires at least three BlueStore OSDs, with each OSD located on a different node.

The OSDs must be located on different nodes, because the failureDomain will be set to host by default, and the erasureCoded chunk settings require at least three different OSDs (two dataChunks + one codingChunks).

  apiVersion: ceph.rook.io/v1
  kind: CephFilesystem
  metadata:
    name: myfs-ec
    namespace: rook-ceph
  spec:
    metadataPool:
      replicated:
        size: 3
    dataPools:
      - erasureCoded:
          dataChunks: 2
          codingChunks: 1
    metadataServer:
      activeCount: 1
      activeStandby: true

These definitions can also be found in the filesystem-ec.yaml file.

The pools allow all of the settings defined in the Pool CRD spec. In the example above, there must be at least three hosts (size three) and at least eight devices (six data + two coding chunks) in the cluster.