Support Policies for RHEL High Availability Clusters - sbd and fence_sbd
Contents
Overview
Applicable Environments
- Red Hat Enterprise Linux (RHEL) 6 or 7 with the High Availability Add-On
Useful References and Guides
- Support policies for RHEL High Availability clusters
- Explore components:
sbd
andfence_sbd
- Design guidance: Using
sbd
for fencing
Introduction
This guide offers Red Hat's policies and requirements around the usage of the fencing components sbd
and fence_sbd
for 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
Available/Supported Releases sbd
is available and supported for usage in RHEL HA clusters using the following package releases:
- RHEL 7 Update 1 or later: Using
pacemaker-1.1.12-22.el7
or later andsbd-1.2.1-3
or later. - RHEL 6 Update 8 or later: Using
pacemaker-1.1.14-8.el6
or later andsbd-1.2.1-9.el6
or later.
Supported releases for sbd
poison-pill fencing via block-device: sbd
provides - and Red Hat Supports - the "poison pill" feature and usage of fence_sbd
as of RHEL 7 Update 4's sbd-1.3.0-3.el7
and fence-agents-sbd-4.0.11-60.el7
. Prior releases of sbd
and fence-agents
do not include this functionality, and thus sbd
is limited to sbd
health and quorum fencing and sbdstonith-watchdog-timeout` fencing in such releases.
Red Hat also supports the usage of sbd
without using poison-pill fencing via block-device. The use of poison-pill increases reliability of sbd
as a STONITH method, but in cases where shared storage is not available or some other reason prevents the usage of poison-pill, Red Hat will support a cluster that uses sbd
without the poison-pill feature.
Storage compatibility sbd
poison-pill fencing via block-device: Red Hat's typical storage compatibility policies for RHEL High Availability apply to sbd
- in that Red Hat does not certify sbd
with specific storage solutions. It is up to customer organizations using sbd
poison-pill fencing via block-device to ensure their storage solution is adequate for shared access across cluster members through all relevant failure scenarios the cluster may need to endure.
- See also: Support policies - Storage compatibility
Storage device requirements for sbd
poison-pill fencing via block-device:
- A block device must be shared by all nodes of the cluster
- All nodes must have write access to the shared device.
- The shared block device cannot host a file system or be used by any other component.
- The shared block device cannot be managed by LVM or incorporated into an LVM volume group.
- The shared block device should not be managed by any RAID, mirroring, or replication that is administered by the cluster members themselves. Any replication employed must be transparent to the hosts.
- 4 Megabytes in size is sufficient for the shared block device.
Storage replication technologies with sbd
poison-pill fencing via block-device: Red Hat does not test specific vendor storage replication technologies that may facilitate cluster-wide access to the block device sbd
poison-pill fencing via block-device. While Red Hat does not prevent organizations from using such technologies, it cannot guarantee that sbd
will function as expected with all of them. It is important for organizations using these technologies to thoroughly test sbd
in conjunction with their chosen solutions, especially through all potential failure scenarios that may create a split between nodes or storage arrays. Storage vendors should be consulted for input on the capabilities of their solutions and how they may perform in connection with RHEL High Availability or sbd
.
Support with pacemaker
only: sbd
is only available and supported for usage when pacemaker
is in use. sbd
is suitable for usage in RHEL 6 clusters with cman
and pacemaker
, as well as RHEL 7 pacemaker
clusters. sbd
is not supported for usage with 6 pure-cman
clusters that do not use pacemaker
.
No support in clusters using pacemaker_remote
: sbd
is not supported in clusters utilizing any "remote" nodes - either baremetal or virtual-machine nodes that utilize pacemaker_remote
.
Suitable watchdog timer (WDT) devices: Red Hat does not maintain a list of supported hardware watchdog timer devices that can be used with sbd
. Red Hat considers a device to be suitable for usage with sbd
if:
- The device is not amongst those specifically highlighted in this policy guide as unsupported
- That device's driver implements the structures, functions, and functionality that are expected of a watchdog timer device as explained within the kernel documentation. Red Hat would consider this true for drivers shipped within a RHEL-supplied kernel, other than
softdog
. - The device is guaranteed to abruptly halt the system if the device is not updated within the timeout period specified to the watchdog device using the kernel's watchdog API.
- The device can be demonstrated to carry out this halting action under the expected circumstances.
Support for virtualization-emulated watchdogs: Red Hat supports usage of sbd
with a libvirt/KVM-provided hardware watchdog using emulated model i6300esb
. Red Hat does not provide support or testing for use of any other emulated watchdog devices (e.g. VMWare). However, if there is interest in another model or device on a different virtualization platform, please contact Red Hat Support to communicate this interest.
No Support for Software-Emulated Watchdog: This watchdog timer device used by sbd
cannot be emulated by software, such as is done by the softdog
driver. Such programs operate within the limitations and available resources provided by the kernel, and thus cannot be guaranteed to carry out the necessary halting action if the operating system is malfunctioning or starved of resources.
Investigations may require confirmation of a suitable device: Because Red Hat does not maintain a list of suitable devices for usage with sbd
and thus may not have extensive knowledge of every device type, questions may arise in the course of investigations as to the suitability of the device in use. If unexpected behavior is observed with sbd
, Red Hat may request and require demonstration of the functionality of the watchdog device in use before it can deeply investigate. In situations where the functionality of the device itself is questionable, Red Hat may require the concerning behavior from sbd
be reproduced on known hardware, or may require investigation from the vendor of the device.
RHEL 6 with QDisk: RHEL 6 clusters utilizing QDisk are not compatible with or supported with sbd
Comments