Document URL: 

https://docs.openshift.com/container-platform/4.2/monitoring/cluster-monitoring/configuring-the-monitoring-stack.html#configuring-persistent-storage

Section Number and Name: 

Unknown

Describe the issue: 

Documentation states the following:

~~~

Prerequisites

- Dedicate sufficient local persistent storage to ensure that the disk does not become full. How much storage you need depends on the number of pods. For information on system requirements for persistent storage, see Prometheus database storage requirements.

- Make sure you have a Persistent Volume (PV) ready to be claimed by the Persistent Volume Claim (PVC), one PV for each replica. Since Prometheus has two replicas and Alertmanager has three replicas, you need five PVs to support the entire monitoring stack. The Persistent Volumes should be available from the Local Storage Operator. This does not apply if you enable dynamically provisioned storage.

- Use the *block* type of storage.

- Configure local persistent storage.

~~~

However, as you can see within BZ#1786779:

~~~
Pawel Krupa 2020-01-06 09:02:06 UTC

Alertmanager and prometheus expect a POSIX filesystem with correct permissions for storage, block devices are not supported.

This needs a documentation fix.
~~~

Suggestions for improvement: 

Maybe completely removing the Block mode prerequisite for the Monitoring stack if non supportable? or put Filesystem mode prerequisite instead?

Additional information: 

In the "local persistent volume claim" section[1] there is also no example of "volumeMode: Block" variable, which makes the config to default to "Filesystem" mode despite previously stating "Block" mode as prerequisite.

[1] - https://docs.openshift.com/container-platform/4.2/monitoring/cluster-monitoring/configuring-the-monitoring-stack.html#configuring-a-local-persistent-volume-claim_configuring-monitoring