Bug 1974844

Summary: [Doc][RBD]- RBD PERSISTENT WRITE-BACK CACHE
Product: [Red Hat Storage] Red Hat Ceph Storage Reporter: Harish Munjulur <hmunjulu>
Component: DocumentationAssignee: ceph-docs <ceph-docs>
Status: CLOSED DUPLICATE QA Contact: Harish Munjulur <hmunjulu>
Severity: high Docs Contact:
Priority: unspecified    
Version: 5.0CC: asakthiv, kdreyer
Target Milestone: ---   
Target Release: 5.0   
Hardware: Unspecified   
OS: Unspecified   
Whiteboard:
Fixed In Version: Doc Type: If docs needed, set a value
Doc Text:
Story Points: ---
Clone Of: Environment:
Last Closed: 2021-06-24 06:21:28 UTC Type: Bug
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:

Description Harish Munjulur 2021-06-22 16:14:10 UTC 
Describe the issue: include documentation of RBD PERSISTENT WRITE-BACK CACHE

Document URL: https://docs.ceph.com/en/latest/rbd/rbd-persistent-write-back-cache/

To enable the persistent write-back cache, the following Ceph settings need to be enabled.:

rbd persistent cache mode = {cache-mode}
rbd plugins = pwl_cache
Value of {cache-mode} can be rwl, ssd or disabled. By default the cache is disabled.

Here are some cache configuration settings:

rbd_persistent_cache_path A file folder to cache data. This folder must have DAX enabled (see DAX) when using rwl mode to avoid performance degradation.

rbd_persistent_cache_size The cache size per image. The minimum cache size is 1 GB.

rbd_persistent_cache_log_periodic_stats This is a debug option. It is used to emit periodic perf stats to the debug log if debug rbd pwl is set to 1 or higher.