Chapter 2. System overview 29
2.5.13  Quorum disks
A quorum disk is an MDisk or a managed drive that contains a reserved area for use 
exclusively by the system. In IBM Storwize V7000, internal drives can be considered as 
quorum candidates. The clustered system uses quorum disks to break a tie when exactly half 
the nodes in the system remain after a SAN failure.
The clustered system automatically forms the quorum disk by taking a small amount of space 
from an MDisk. It allocates space from up to three different MDisks for redundancy, although 
only one quorum disk is active.
If the environment has multiple storage systems, allocate the quorum disk on different storage 
systems to avoid the possibility of losing all of the quorum disks because of a failure of a 
single storage system. It is possible to manage the quorum disks by using the CLI.
2.5.14  IP Quorum
In a HyperSwap configuration, there must be a third, independent site to house quorum 
devices. To use a quorum disk as the quorum device, this third site must use Fibre Channel 
connectivity with an external storage system. Sometimes, Fibre Channel connectivity is not 
possible. In a local environment, no extra hardware or networking, such as Fibre Channel or 
SAS-attached storage, is required beyond what is normally always provisioned within a 
system.
To use an IP-based quorum application as the quorum device for the third site, no Fibre 
Channel connectivity is used. Java applications are run on hosts at the third site. However, 
strict requirements on the IP network exist, and some disadvantages with the use of 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 from the system, or when node service IP addresses are 
changed.
For stable quorum resolutions, an IP network must provide the following requirements: 
/SM590000Connectivity from the hosts to the service IP addresses of all nodes. If IP quorum is 
configured incorrectly, the network must also deal with possible security implications of 
exposing the service IP addresses because this connectivity can also be used to access 
the service GUI. 
/SM590000Port 1260 is used by IP quorum applications to communicate from the hosts to all nodes. 
/SM590000The maximum round-trip delay must not exceed 80 ms, which means 40 ms in each 
direction. 
/SM590000A minimum bandwidth of 2 MBps is ensured for node-to-quorum traffic. 
Even with IP quorum applications at the third site, quorum disks at site one and site two are 
required because they are used to store metadata. To provide quorum resolution, use the 
mkquorumapp command to generate a Java application that is copied from the system and run 
on a host at a third site. The maximum number of applications that can be deployed is five. 
Currently, supported Java runtime environments (JREs) are IBM Java 7.1 and IBM Java 8.