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TECH169366_VMware_IO_fencing_2011-09-12

Symantec Support for I/O fencing with Storage Foundation High Availability (SFHA) and Storage Foundation Cluster File System (SFCFS) clusters of VMware Virtual Machines

1.Introduction to I/O fencing

I/O fencing is a feature that prevents data corruption in the event of a communication failure in a SFHA/SFCFS cluster. I/O Fencing consists of two components, Membership Arbitration and Data Protection.

Membership Arbitration allows only one of multiple partitions to continue operation in case of a network partition. The I/O fencing module uses coordination points such as SCSI3 compliant disks or Coordination Point Servers (CP Servers) for membership arbitration. At the time of a network

partition each partition races for the coordination points, and the partition that grabs the majority of coordination points survives whereas nodes from all other partitions panic.

Data Protection allows write access only for members of the cluster which survive after arbitration.

It blocks access to storage from non-members so that even a node that is accidently alive is unable to cause damage. Traditionally I/O fencing uses SCSI3 Persistent Reservation (SCSI3-PR) to ensure that the I/O operations from the losing node cannot reach a disk that the surviving partition has taken over.

For details please refer to the following documentation :

a)I/O Fencing White Paper on Symantec Connect

https://www.wendangku.net/doc/e1486090.html,/connect/articles/veritas-cluster-server-io-fencing-deployment-

considerations

b)Relevant sections in the Veritas Cluster Server Installation Guide

“About I/O fencing”

https://https://www.wendangku.net/doc/e1486090.html,/public/documents/vcs/5.1sp1/linux/productguides/html/vcs_install/ ch01s03s03.htm

“About configuring VCS clusters for data integrity”

https://https://www.wendangku.net/doc/e1486090.html,/public/documents/vcs/5.1sp1/linux/productguides/html/vcs_install/ ch01s06.htm

2.What has been supported prior to this tech note for Virtual Environments?

In virtualized environments that do not support SCSI3-PR, I/O fencing attempts to provide

reasonable safety for the data disks. SFHA/SFCFS require you to configure non-SCSI3 server-based I/O fencing in such environments. Non-SCSI3 fencing uses CP servers as coordination points with some additional configuration changes to support I/O fencing in such environments.

3. What support is introduced by this tech note?

This tech note introduces support for SCSI3 I/O fencing with SFHA and SFCFS clusters of VMware Virtual Machines subject to the following considerations. Both disk-based I/O fencing1 and server-based I/O fencing2 are supported. SCSI3 I/O fencing requires that all data and coordinator disks support SCSI3-PR.

Table 1: Supported Versions

4.Required Patches:

The following VMware patch is required with VMware ESX 4.1

https://www.wendangku.net/doc/e1486090.html,/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externa lId=2000604

5.Block Storage Allocation:

Block Storage must be allocated to the Virtual Machines using Raw Device Mapping in Pass-through Mode(RDM-P).

1 I/O fencing that uses coordinator disks is referred to as disk-based I/O fencing.

2I/O fencing that uses at least one CP server system is referred to as server-based I/O fencing.

6.Restrictions :

Each SFHA/SFCFS cluster should have no more than one Virtual Machine from each physical server.

However, a physical server can host more than one Virtual Machine as long as they do not belong to the same cluster.

Figure 1: Supported Cluster Configuration

Figure 2: Unsupported Cluster Configuration

For example, consider two ESX Servers Server A and Server B with two Virtual Machines created on each Server: VM_A_1 and VM_A_2 on Server A and VM_B_1 and VM_B_2 on Server B. You can create two clusters : Cluster 1 with VM_A_1 and VM_B_1 and Cluster 2 with VM_A_2 and VM_B_2.

However you cannot create a cluster with both VM_A_1 and VM_A_2. Similarly you cannot create a cluster with both VM_B_1 and VM_B_2.

Please ensure that one set of coordinator disks is made available to only one Virtual Machine per ESX server. You must use a unique set of coordinator disks for each cluster. Symantec does not support assigning coordinator disks of one cluster to another cluster.

7.Hardware Compatibility List (HCL) Requirements

The array used for housing the coordinator disks should be in the Symantec HCL for 5.1SP1 listed under the Operating System running inside the VMware Virtual Machine (Linux Red Hat). The HCL is available via the Symantec Operations Readiness Tools (SORT) website at the following link :

https://www.wendangku.net/doc/e1486090.html,/business/support/index?page=content&id=TECH74012

8.Running vxfentsthdw

Please run vxfentsthdw to confirm that the array meets the I/O fencing requirements. Please see section “Testing the disks using vxfentsthdw utility” in the Veritas Cluster Server Installation Guide

https://https://www.wendangku.net/doc/e1486090.html,/public/documents/vcs/5.1sp1/linux/productguides/html/vcs_install/ch0 9s01s03s03.htm

It is not required to install SFHA/SFCFS in order to run this utility. vxfentsthdw(1m) is available on the 5.1SP1 DVD in the cluster_server/tools directory.

9.What is not supported?

VMware currently does not support SCSI3-PR with N-Port ID Virtualization (NPIV). Consequently, SCSI3 I/O fencing support in SFHA and SFCFS is restricted to block storage allocated in RDM-P mode.

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