- Red Hat Enterprise Linux (RHEL) 6, 7, or 8 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 using the following package releases:
- RHEL 8: All package releases
- RHEL 7 Update 1 or later: Using
pacemaker-1.1.12-22.el7or later and
- RHEL 6 Update 8 or later: Using
pacemaker-1.1.14-8.el6or later and
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
fence-agents-sbd-4.0.11-60.el7, and all releases in RHEL 8. Prior releases of
fence-agents do not include this functionality, and thus
sbd is limited to
sbd health and quorum fencing and sbd
stonith-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.
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 in clusters using
sbd is not supported in clusters utilizing any "remote" nodes - either baremetal or virtual-machine nodes that utilize
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.
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 that RHEL High Availability is available on.
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