Merge pull request #8145 from pavilalopes/update-docs

docs: clarify resource documentation

Documentation/ceph-cluster-crd.md

@@ -537,9 +537,8 @@ This allows to keep Rook components running when for example a node runs out of
 You can set resource requests/limits for Rook components through the [Resource Requirements/Limits](#resource-requirementslimits) structure in the following keys:
 
 * `mon`: Set resource requests/limits for mons
-* `osd`: Set resource requests/limits for OSDs
-  This key applies for all OSDs regardless of their device classes. In case of need to apply resource requests/limits for OSDs with
-  particular device class use specific osd keys below.
+* `osd`: Set resource requests/limits for OSDs.
+  This key applies for all OSDs regardless of their device classes. In case of need to apply resource requests/limits for OSDs with particular device class use specific osd keys below. If the memory resource is declared Rook will automatically set the OSD configuration `osd_memory_target` to the same value. This aims to ensure that the actual OSD memory consumption is consistent with the OSD pods' resource declaration.
 * `osd-<deviceClass>`: Set resource requests/limits for OSDs on a specific device class. Rook will automatically detect `hdd`,
   `ssd`, or `nvme` device classes. Custom device classes can also be set.
 * `mgr`: Set resource requests/limits for MGRs
@@ -559,11 +558,12 @@ If a user configures a limit or request value that is too low, Rook will still r
 * `mon`: 1024MB
 * `mgr`: 512MB
 * `osd`: 2048MB
-* `mds`: 4096MB
 * `prepareosd`: 50MB
 * `crashcollector`: 60MB
 * `mgr-sidecar`: 100MB limit, 40MB requests
 
+> **HINT** The resources for MDS daemons are not configured in the Cluster. Refer to the [Ceph Filesystem CRD](ceph-filesystem-crd.md) instead.
+
 ### Resource Requirements/Limits
 
 For more information on resource requests/limits see the official Kubernetes documentation: [Kubernetes - Managing Compute Resources for Containers](https://kubernetes.io/docs/concepts/configuration/manage-compute-resources-container/#resource-requests-and-limits-of-pod-and-container)

Documentation/ceph-filesystem-crd.md

@@ -127,5 +127,14 @@ The metadata server settings correspond to the MDS daemon settings.
 * `annotations`: Key value pair list of annotations to add.
 * `labels`: Key value pair list of labels to add.
 * `placement`: The mds pods can be given standard Kubernetes placement restrictions with `nodeAffinity`, `tolerations`, `podAffinity`, and `podAntiAffinity` similar to placement defined for daemons configured by the [cluster CRD](https://github.com/rook/rook/blob/{{ branchName }}/cluster/examples/kubernetes/ceph/cluster.yaml).
-* `resources`: Set resource requests/limits for the Filesystem MDS Pod(s), see [Resource Requirements/Limits](ceph-cluster-crd.md#resource-requirementslimits).
+* `resources`: Set resource requests/limits for the Filesystem MDS Pod(s), see [MDS Resources Configuration Settings](#mds-resources-configuration-settings)
 * `priorityClassName`: Set priority class name for the Filesystem MDS Pod(s)
+
+### MDS Resources Configuration Settings
+
+The format of the resource requests/limits structure is the same as described in the [Ceph Cluster CRD documentation](ceph-cluster-crd.md#resource-requirementslimits).
+
+If the memory resource limit is declared Rook will automatically set the MDS configuration `mds_cache_memory_limit`. The configuration value is calculated with the aim that the actual MDS memory consumption remains consistent with the MDS pods' resource declaration.
+
+In order to provide the best possible experience running Ceph in containers, Rook internally recommends the memory for MDS daemons to be at least 4096MB.
+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.