IP quorum configuration

The IP quorum application is a Java™ application that runs on a separate server or host. An IP quorum application is used in Ethernet networks to resolve failure scenarios where half the nodes or enclosures on the system become unavailable. In this scenario, the application determines which nodes or enclosures can continue processing host operations and avoids a split system, where both halves of the system continue to process I/O independently.

In stretched configurations or HyperSwap® configurations, an IP quorum application can be used at the third site as an alternative to third-site quorum disks. No Fibre Channel connectivity at the third site is required to use an IP quorum application as the quorum device. If you currently have a third-site quorum disk, you must remove the third site before you use an IP quorum application.

There are strict requirements on the IP network and some disadvantages with using an IP quorum application. When certain aspects of the system configuration change, an IP quorum application must be reconfigured and redeployed to hosts. These aspects include adding or removing a node (or hot-spare node) from the system or when service IP addresses are changed on a node. Other examples include changing the system certificate or experiencing an Ethernet connectivity issue. An Ethernet connectivity issue prevents an IP quorum application from accessing a node that is still online. If an IP application is offline, the IP quorum application must be reconfigured because the system configuration changed. To view the state of an IP quorum application in the management GUI, select Settings > System > IP Quorum. You can also use the lsquorum command to view the state of the IP quorum application.

Even with an IP quorum application at the third site, quorum disks at site one and site two are required, as they are used to store metadata that restores system configuration during failure scenarios. Quorum disks for each site are selected automatically and can be configured in the management GUI by selecting Pools > MDisks by Pools. You can also use the chquorum command to assign MDisk as a quorum disk.

An IP quorum application can also act as the quorum device for systems that are configured with a single-site or standard topology that does not have any external storage configured. This configuration gives a system tie-break capability, automatically resuming I/O processing if half of the system's nodes or enclosures are inaccessible.

The maximum number of IP quorum applications that can be deployed is five. However, multiple instances of the IP quorum application cannot be run on the same host or server. Only one instance of the IP quorum application per host or server is supported. IP quorum applications on multiple hosts or servers can be configured to provide redundancy.

Do not deploy the IP quorum application on a host that depends on storage that is presented by the system. This action can result in a situation where the nodes need to detect the IP quorum application to process I/O, but cannot because the IP quorum application cannot access storage.

IP quorum requirements

For stable quorum resolutions, an IP network must provide the following requirements:

Connectivity from the servers that are running an IP quorum application to the service IP addresses of all nodes or node canisters. The network must also deal with possible security implications of exposing the service IP addresses, as this connectivity can also be used to access the service assistant interface if the IP network security is configured incorrectly.
On each server that runs an IP quorum application, ensure that only authorized users can access the directory that contains the IP quorum application.
Port 1260 is used by the IP quorum application to communicate from the hosts to all nodes or enclosures.
The maximum round-trip delay must not exceed 80 milliseconds (ms), which means 40 ms each direction.
A minimum bandwidth of 2 megabytes per second is guaranteed for traffic between the system and the quorum application.

The following minimum requirements must be met on the hosts that are used to run an IP quorum application:

Table 1. Supported Operating Systems and Java Runtime Environments
Operating System	Java™ Vendor and Version
	IBM®				OpenJDK				Oracle
	7.1	7.1+	8	8.1+	7	7+	8	8+	7	7+	8	8+
AIX7	X	X	X	X
AIX7.x	X	X	X	X
RHEL6	X	X	X	X	X	X	X	X	X	X	X	X
RHEL6.x	X	X	X	X	X	X	X	X	X	X	X	X
RHEL7	X	X	X	X	X	X	X	X	X	X	X	X
RHEL7.x	X	X	X	X	X	X	X	X	X	X	X	X
SLES11	X	X	X	X	X	X	X	X	X	X	X	X
SLES11.x	X	X	X	X	X	X	X	X	X	X	X	X
SLES12	X	X	X	X	X	X	X	X	X	X	X	X
SLES12.x	X	X	X	X	X	X	X	X	X	X	X	X
CentOS6					X	X	X	X
CentOS6.x					X	X	X	X
CentOS7					X	X	X	X
CentOS7.x					X	X	X	X
Win2008	X	X			X	X	X	X	X	X	X	X
Win2008x	X	X			X	X	X	X	X	X	X	X
Win2012	X	X	X	X	X	X	X	X	X	X	X	X
Win2012x	X	X	X	X	X	X	X	X	X	X	X	X
Win2016	X	X	X	X	X	X	X	X	X	X	X	X
Win2016x	X	X	X	X	X	X	X	X	X	X	X	X

Installing IP quorum

If you change the configuration by adding a node, changing a service IP address, or changing SSL certificates, you must download and install the IP quorum application again. To download and install the IP quorum application, complete the following steps:

In the management GUI, select Settings > System > IP Quorum and download the version of the IP quorum Java application. You can also use the command-line interface (CLI) to enter the mkquorumapp command to generate an IP quorum Java application. The application is stored in the dumps directory of the system with the file name ip_quorum.jar.
On the server or host on which you plan to run the IP quorum application, create a separate directory that is dedicated to the IP quorum application.
Transfer the IP quorum application from the system to a separate directory on the server or host that is to run the IP quorum application.
Use the ping command on the host server to verify that it can establish a connection with the service IP address of each node in the system.
On the host, run the command java -jar ip_quorum.jar to initialize the IP quorum application.
To verify that the IP quorum application is installed and active, select Settings > System > IP Quorum. The new IP quorum application is displayed in the table of detected applications. The system automatically selects MDisks for quorum disks. In a stretched or HyperSwap configuration with IP quorum, the system automatically selects an MDisk from both sites. These MDisks store metadata that are used for system recovery. If you want to select a specific MDisk to use as quorum disks, select MDisk by Pools and right-click the MDisk and select Quorum > Modify Quorum Disk. You can also use the lsquorum command on the system CLI to verify that the IP quorum application is connected and is the active quorum device. If you want to modify the MDisk that are used for quorum by using the command-line interface, use the chquorum command.