You can list the quorum disk candidates and the active quorum disk in a system by using the  lsquorum  command. When the set of quorum disk candidates is chosen, it is fixed. However, a new quorum disk  candidate can be chosen in one of the following conditions: An offline MDisk is not replaced as a quorum disk candidate. For disaster recovery purposes, a system must be regarded as a single entity so that the  system and the quorum disk must be colocated.  Special considerations are required for the placement of the active quorum disk for a  stretched or split cluster and split I/O Group configurations. For more information, see IBM  Knowledge Center. Important:  Running an SVC system without a quorum disk can seriously affect your  operation. A lack of available quorum disks for storing metadata prevents any migration  operation (including a forced MDisk delete). Mirrored volumes can be taken offline if no quorum disk is available. This behavior occurs  because the synchronization status for mirrored volumes is recorded on the quorum disk. During the normal operation of the system, the nodes communicate with each other. If a node  is idle for a few seconds, a heartbeat signal is sent to ensure connectivity with the system. If a  node fails for any reason, the workload that is intended for the node is taken over by another  node until the failed node is restarted and readmitted into the system (which happens  automatically). If the Licensed Internal Code on a node becomes corrupted, which results in a failure, the  workload is transferred to another node. The code on the failed node is repaired, and the  node is readmitted into the system (which is an automatic process). In a stretched configuration or HyperSwap configuration, you must use a third, independent  site to house quorum devices. To use a quorum disk as the quorum device, this third site must  use Fibre Channel or IP connectivity together with an external storage system. 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,  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 from the system, or when node service IP addresses are  changed.  IP quorum configuration GLYPH<SM590000> When the administrator requests that a specific MDisk becomes a quorum disk by using  the  chquorum  command GLYPH<SM590000> When an MDisk that is a quorum disk is deleted from a storage pool GLYPH<SM590000> When an MDisk that is a quorum disk changes to image mode Chapter 2. System overview  27