fence_scsi on VMware vCenter / ESXi fails when a cluster node is shutdown from the host in RHEL 5 or 6 or 7

Solution Verified - Updated

Environment

  • Red Hat Enterprise Linux (RHEL) 5 or 6 or 7 with the High Availability Add On
  • VMware vCenter / ESXi 5.0 or 5.1
  • VMs using shared storage presented via Virtual Disk Files (VMDKs) or Raw Device Mapping (RDM)
  • SCSI Persistent Reservation Fencing (fence_scsi)

Issue

  • When shutting down a cluster node from vCenter, the node fails to be fenced by fence_scsi
  • When a VMware cluster node is shutdown gracefully, its SCSI registrations and reservations disappear on their own
  • When simulating a failure scenario where the active node providing service is shut down forcefully, the backup node does not take over the service.

Resolution

See the following document on fence_scsi and fence_mpath support compatibility for VMware Virtual Machines:

Root Cause

  • VMware ESXi's platform does not completely implement the SCSI-3 specification, and SPC-3-style persistent reservations on this platform are handled differently than would be on a typical physical SCSI-3-compatible storage array. Specifically, when a VM is shutdown, either from its own operating system or from the virtualization host (such as via vCenter), the ESXi host will actually remove that VM's registrations and reservations from the storage devices presented to it. This breaks the logic used by fence_scsi, which expects to find the registration for the VM that would have been set up during unfencing (RHEL 6) or when scsi_reserve started (RHEL 5). There is no way for the fence_scsi agent to safely accommodate this unexpected behavior, and so the fencing operation simply fails.

  • You may wish to contact VMware technical support for more information on the implementation of the SCSI-3 specification and any limitations that may exist therein with regards to SPC-3 Persistent Reservations.

SBR
Product(s)
Components
Category
Tags

This solution is part of Red Hat’s fast-track publication program, providing a huge library of solutions that Red Hat engineers have created while supporting our customers. To give you the knowledge you need the instant it becomes available, these articles may be presented in a raw and unedited form.