IP quorum configuration

In some HyperSwap^® configurations, IP quorum applications 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. The IP quorum application is a Java application that runs on a host at the third site. The IP network is used for communication between the IP quorum application and node canisters in the system. 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 IP quorum applications. Unlike quorum disks, all IP quorum applications must be reconfigured and redeployed to hosts when certain aspects of the system configuration change. These aspects include adding or removing a node canister from the system or when node service IP addresses are changed. 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 IP quorum applications at the third site, quorum disks at site one and site two are required, as they are used to store metadata. 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 standard topology that do 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 node canisters are inaccessible.

The maximum number of IP quorum applications that can be deployed is five. Applications can be deployed on multiple hosts to provide redundancy.

Do not deploy the IP quorum application on a host that depends on storage that is presented by the system. Doing so might result in a deadlock situation where the nodes in the system need to detect the IP quorum application to process I/O, but the IP quorum application needs to access storage on the system to answer.

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 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.
Port 1260 is used by IP quorum applications to communicate from the hosts to all node canisters.
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 node canister-to-quorum traffic.

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

Supported operating systems:
- Red Hat Enterprise Linux 6.5, Red Hat Enterprise Linux 7
- SUSE Linux Enterprise Server 11m3, SUSE Linux Enterprise Server 12
Supported Java Runtime Environments: IBMJava 7.1, IBMJava 8

Installing IP quorum

If you change the configuration by adding an enclosure, 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 click either Download IPv4 Application or Download IPv6 Application to create 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.
Transfer the IP quorum application from the system to a directory on the host that is to run the IP quorum application.
Use the ping command on the host to verify that it can establish a connection with the service IP address of each node canister in the system.
On the host, use 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 system automatically selects MDisks for quorum disks. In a 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 specific MDisk to use as quorum disks, select MDisk by Pools and right-click the MDisk and select Quorum > Modify Quorum Disk. The new IP quorum application is displayed in the table of detected applications. 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.