Support Policies for RHEL Resilient Storage - dlm General Policies

Updated -

Contents

Overview

Applicable Environments

  • Red Hat Enterprise Linux (RHEL) with the Resilient Storage Add-On

Useful References and Guides

Introduction

This guide lays out Red Hat's policies applicable to the use of the Distributed Lock Manager - dlm - in RHEL Resilient Storage deployments. Users of dlm in RHEL Resilient Storage clusters should adhere to these policies in order to be eligible for assistance from Red Hat Support with the appropriate product support subscriptions.

Policies

Maximum number of nodes supported by DLM: The maximum number of nodes when using DLM is 16 nodes as stated in: What is the supported number of nodes for a RHEL 7 or 8 Resilient Storage cluster?

dlm unsupported with RRP / SCTP in RHEL 6 or 7: Red Hat does not support the usage of dlm or dlm-using components when dlm is configured to use SCTP communications - also known as "multi-homing" - or when the cluster is configured to use Redundant Ring Protocol (RRP). Such configurations are likely to behave in unexpected ways.

  • rgmanager in RHEL 6 must use cpglockd instead of dlm in clusters where RRP is configured in order to receive support from Red Hat. RHEL 6 with rgmanager will automatically enable this alternate lock manager - cpglockd - when the cluster is configured for RRP.

  • Resilient Storage components that rely on dlm are not supported by Red Hat in RRP configurations on RHEL 6 or RHEL 7. Neither gfs2 nor cmirrord is supported in clusters configured for RRP.

dlm only supports clusters with one interface in RHEL 8: Red Hat does not support the usage of dlm or dlm-using components with more than one ring configured in a RHEL 8 cluster using the knet transport. Such configurations are likely to behave in unexpected ways.

Any Resilient Storage cluster that uses dlm, lvmlockd, or gfs2 must be configured with only a single ring in the cluster in order to receive support from Red Hat. Red Hat recommends utilizing bonding or teaming for the interfaces in that single cluster ring as the method to achieve redundancy.

Fencing required: Usage of dlm in a cluster requires that fencing be configured with a proper storage or power device, or sbd. Red Hat does not support clusters actively using dlm that do not have fencing configured and a proper STONITH/fencing method configured for each node.

  • See also: Support policies: General requirements for fencing/STONITH
  • In the above fencing/STONITH policies guide, an allowance is made for clusters without shared storage to use "alternative" fence methods. This is not allowed for clusters utilizing dlm for any component - even if shared storage is not involved. dlm-using clusters must have a STONITH method that will power a node off or cut off a node from shared resources when there is a problem.

RHEL 7 and 8: Usage of systemd dlm.service: Red Hat does not support starting or managing dlm in RHEL 7 or 8 via the systemd dlm.service unit that is provided by the dlm package. The dlm_controld daemon should be started and managed using an ocf:pacemaker:controld resource within the cluster.

dlm not supported on pacemaker-remote "remote-nodes": When a cluster contains remote-nodes offered via pacemaker-remote, dlm is not supported by Red Hat to be used on any such remote-node. Any controld resource and anything dependent on it that uses dlm should be constrained to never run on any remote-node.

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