Support Policies for RHEL High Availability Clusters - LVM in a Cluster

Contents

• Overview
  • Applicable Environments
  • Useful References and Guides
  • Introduction
• Policies

Overview

Applicable Environments

• Red Hat Enterprise Linux (RHEL) with the High Availability Add-On

Useful References and Guides

• Support Policies for RHEL High Availability Clusters

Introduction

This guide offers Red Hat's policies around the usage of LVM within RHEL High Availability clusters. Users of RHEL High Availability clusters should adhere to these policies in order to be eligible for support from Red Hat with the appropriate product support subscriptions.

Policies

Cluster management of shared LVM: Clusters that share block storage devices and manage them with LVM must use one of the following methods for managing shared access to these devices in order to receive support from Red Hat:

• HA-LVM: Shared LVM volumes are activated by the cluster resource manager using an LVM or LVM-activate resource (with pacemaker) or lvm resource (with rgmanager). When using LVM resource and not managed by clvmd or controld resource, then /etc/lvm.conf attribute should be set tolocking_type=1.
• lvmlockd in RHEL 8 Resilient Storage clusters with /etc/lvm.conf attribute set to locking_type=1.
• clvmd in RHEL 6 or 7 Resilient Storage clusters with /etc/lvm.conf attribute set to locking_type=3.

Red Hat may be unable to provide support with cluster environments sharing LVM devices that do not use one of these facilities.

LVM RAID: Red Hat's support of shared LVM RAID volumes - volumes using any "raid" segment type for mirroring - in a High Availability cluster is subject to the following conditions:

• RHEL 8 with the LVM-activate resource type: Supported by Red Hat
• RHEL 7 with the LVM or LVM-activate resource type: Supported by Red Hat with resource-agents-3.9.5-54.el7 or later, only when using tagging with a volume_list.
• RHEL 6 with pacemaker and the LVM resource type: Supported by Red Hat with resource-agents-3.9.5-34.el6 or later, only when using tagging with a volume_list.
• RHEL 6 with rgmanager and the lvm resource type: Supported by Red Hat with resource-agents-3.9.2-21.el6 or later, only when using tagging with a volume_list.
• Any RHEL release while using lvmlockd or clvmd from Resilient Storage: Red Hat does not support usage of LVM RAID volumes with these clustered-LVM managers

LVM mirroring (non-RAID): Red Hat supports usage of clustered LVM mirrored volumes - those of the segment type mirror - within RHEL High Availability clusters.

• RHEL 6: Supported with clvmd that managed the clustered logical volumes.
• RHEL 7: Supported with clvmd via the clvm resource-agent that managed the clustered logical volumes.
• RHEL 8: The daemon cmirrord is deprecated and is incompatible with resource-agent lvmlockd that is used to managed shared LVM volume groups on RHEL 8+. To use pvmove on a shared volume group on RHEL 8 then see the following article: How to pvmove a volume that utilizes lvmlockd shared activation on RHEL 8?

Use of cache logical volumes in a cluster: Red Hat supports cache volumes in RHEL 8, in RHEL 7.1 or later and RHEL 6.7 or later.

Cache volumes can only be deployed in non-clustered volume groups - that is, VGs that are managed via an HA-LVM system through an LVM or LVM-activate resource (pacemaker) or lvm resource (rgmanager). Cache volumes are not supported with lvmlockd or clvmd from the the Resilient Storage Add-On.

Cache volumes shared by a cluster must use writethrough cache mode by way of allocation { cache_mode = "writethrough" } in /etc/lvm/lvm.conf.

lvm2-lvmetad: With releases of lvm2 that provide support for lvm2-lvmetad, clusters sharing access to LVM volumes must have lvm2-lvmetad disabled in the configuration and as a service to prevent problems resulting from inconsistent metadata caching throughout the cluster.

• RHEL 8: The use of lvm2-lvmetad is deprecated and not supported and the attribute use_lvmetad no longer exists in /etc/lvm/lvm.conf and the the systemd service lvm2-lvmetad no longer exists.
• RHEL 6, 7: lvm2-lvmetad can be disabled in /etc/lvm/lvm.conf in the global section with use_lvmetad=0.

• RHEL 7: lvm2-lvmetad can be disabled and stopped at a service level using systemctl:

  # systemctl disable lvm2-lvmetad
  # systemctl stop lvm2-lvmetad
  

• RHEL 6: lvm2-lvmetad can be disabled at stopped at a service level using chkconfig and service:

  # chkconfig lvm2-lvmetad off
  # service lvm2-lvmetad stop
  

RHEL 6 ocf:heartbeat:LVM resources with exclusive=true and clvmd: The ocf:heartbeat:LVM resource type in RHEL 6 pacemaker clusters must only be used with non-clustered volume groups if the resource must be exclusively-activated (using attribute exclusive=true). Red Hat does not support the usage of LVM resources with exclusive=true managing a clustered volume group in RHEL 6. Exclusive volume groups must use the tagging method of HA-LVM management, which is achieved by ensuring the volume group does not have the clustered attribute enabled on it.

Related Solutions

• Can I use utilize clustered LVM volumes with clvmd and Pacemaker in a RHEL 6 or 7 High Availability cluster?
• How should I configure my RHEL Resilient Storage cluster to manage active/passive shared LVM volumes when I also need to manage active/active LVM volumes for GFS2?