Description of problem: Customers who configure a cluster with only two nodes and use fence scsi do not realize that two member configurations are not supported, as there are problems with network partitions. Version-Release number of selected component (if applicable): RHEL5 How reproducible: Steps to Reproduce: 1. 2. 3. Actual results: No documentation on fence_scsi limitations.... Expected results: Docs with such information: 4 Limitations In addition to these requirements, fencing by way of SCSI persistent reservations also some limitations. --Multipath devices are currently only supported for RHEL 5.0 and later with the use of device-mapper-multipath. --All nodes in the cluster must have a consistent view of storage. In other words, all nodes in the cluster must register with the same devices. This limitation exists for the simple reason that each node must be able to remove another node's registration key from all the devices that it registered with. I order to do this, the node performing the fencing operation must be aware of all devices that other nodes are registered with. If all cluster nodes have a consistent view of storage, this requirement is met. --Devices used for the cluster volumes should be a complete LUN, not partitions. SCSI persistent reservations work on an entire LUN, meaning that access is controlled to each LUN, not individual partitions. --As with other SAN fencing agents, fence_scsi cannot be used in a 2-node cluster. Additional info:
I'm looking at how we might add this list of limitations as a note to the section of the cluster admin guide where we mention that SCSI fencing is one of the fence devices that you can configure (although we don't currently document much more than that). We also provide a table of fence SCSI parameters, and I can reference the limitations there as well, or at least point to where we describe them. But my question is: Should this information go in the fence_scsi man page? That is currently where SCSI fencing is documented, and is probably where people go for information on configuring SCSI fencing.
I have opened BUG 510042 as a separate bug to note that these limitations are not documented in the fence_scsi man page.
The fence_scsi limitations are documented here, it turns out: http://sources.redhat.com/cluster/wiki/SCSI_FencingConfig So the issue may be how to be sure people see that info.
Release note added. If any revisions are required, please set the "requires_release_notes" flag to "?" and edit the "Release Notes" field accordingly. All revisions will be proofread by the Engineering Content Services team. New Contents: *** DRAFT *** Need to create kbase article based on: http://sources.redhat.com/cluster/wiki/SCSI_FencingConfig And mention this kbase in release notes *** DRAFT ***
Changed component to Cluster_Administration. The previous component selected was not specific enough.
I have filed BUG 510353 to separate out the kbase article request from this bug. This bug will be closed when I add the information to the Cluster Admin Guide.
Deleted Release Notes Contents. Old Contents: *** DRAFT *** Need to create kbase article based on: http://sources.redhat.com/cluster/wiki/SCSI_FencingConfig And mention this kbase in release notes *** DRAFT ***
To jwest: I have added a note about SCSI fence limitations in two places to a draft version of a RHEL 5.3 update of the cluster admin guide, which are the places we mention SCSI fencing. - Section 3.5, Configuring Fence Devices, in the chapter on Configuring Red Hat Cluster with Conga. I will attach this to the next comment as fencedevice1.ps. - At the end of Table B.15 in Appendix B, where we list the parameters for the fence devices. I will attach this to a subsequent comment as fencedevice2.ps.
Created attachment 354546 [details] First page to review from admin guide
Created attachment 354547 [details] Second page to review from admin guide
To jwest: Let me know if this description is ok and I'll check this in and try to get this pushed out to redhat.com asap.
Fix is being applied to version 5.3; changing version to 5.3
Changes checked in. Requested push to redhat.com docs page.
Updated document is available. Changes listed as attachments earlier are in section 3.5 and appendix B on the redhat.com docs page: http://www.redhat.com/docs/manuals/enterprise/#RHEL5