- Red Hat Enterprise Linux (RHEL) with the High Availability Add-On
Useful References and Guides
- Support policies for RHEL High Availability clusters
- Explore components:
- Design guidance: Using
This guide offers Red Hat's policies and requirements around the usage of the fencing components
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.
sbd is available and supported for usage in RHEL HA clusters under the following conditions:
- RHEL 8: Supported by Red Hat
- RHEL 7: Supported by Red Hat with RHEL 7.1 or later - using
pacemaker-1.1.12-22.el7or later and
- RHEL 6: Supported by Red Hat with RHEL 6.8 or later - using
pacemaker-1.1.14-8.el6or later and
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 is only available and supported for usage when
pacemaker is in use.
sbd is suitable for usage in RHEL 6 clusters with
pacemaker, as well as RHEL 7 and 8
sbd is not supported for usage with 6 pure-
cman clusters that do not use
No support for sbd on
sbd is not supported on pacemaker remote nodes - either baremetal or virtual-machine nodes that utilize
pacemaker_remote. Prior to RHEL 8.5, to use a watchdog-only SBD configuration, all nodes in the cluster had to use SBD. That prevented using SBD in a cluster where some nodes support it but other nodes (often remote nodes) required some other form of fencing. On RHEL 8.5 or later a cluster that has pacemaker remote nodes can utilize sbd on the cluster nodes (not the remote nodes).
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
- 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
- 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.
- SBD is not supported on VMware. The reason that SBD is not supported in a VMware environment is due to the potential for data corruption if a watchdog does not fire. There can be certain circumstances where the VMware watchdog may not fire (live migration, disk IO, other software issues) which can cause a split brain situation where a node may incorrectly determine that the other nodes have been powered off and attempt to recover services leading to data corruption or other non-desirable behavior.
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 compatibility with cloud platforms: Red Hat does not provide support for
fence_sbd on any of the various cloud-platforms where RHEL High Availability is available.
As noted in other policies above,
sbd is only supported with a suitable hardware watchdog timer - which none of the supported cloud platforms offer at this time - and
sbd is not supported with
The sole exception is SAP Hana on Azure (Large Instances). These are not cloud VMs but rather bare-metal systems managed through the Azure interface. For
sbd to be supported on this platform, an IPMI watchdog must be configured and enabled on each system as documented in the the Configure Watchdog section of the Microsoft documentation. See also: