In some HyperSwap® configurations, IP quorum
applications can be used at the third site as an alternative to third-site quorum
disks.
To use a quorum disk as the quorum device, this third site must use Fibre Channel
connectivity together with an external storage system.
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.
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.
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.
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.
IP quorum requirements
For stable quorum resolutions, an IP network must provide the following requirements:
- Connectivity from the hosts 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 GUI if IP quorum
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: IBM Java 7.1, IBM Java 8
Installing IP quorum
To install and deploy the IP quorum application, complete the following steps:
- 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.
- Use the lsquorum command on the system CLI to verify that the IP quorum
application is connected and is the active quorum device.