Note:  IP Quorum allows the user to replace a third-site Fibre Channel-attached quorum disk with an IP Quorum application. The Java application runs on a Linux host and is used to resolve split-brain situations. Quorum disks are still required in sites 1 and 2 for cookie crumb and metadata. The application can also be used with clusters in a standard topology configuration, but the primary use case is a customer with a cluster split over two sites (stretched or HyperSwap). 

You need Java to run the IP quorum. Your Network must provide as least < 80 ms round-trip latency. All nodes need a service IP address, and all service IP addresses must be pingable from the quorum host. The maximum number of IP quorum applications that can be deployed is five. Applications can be deployed on multiple hosts to provide redundancy. 

## 1.6.8 Storage pools 

A  storage pool  (up to 1024 per system) is a collection of MDisks (up to 128) that are grouped to provide capacity for volumes. All MDisks in the pool are split into extents of the same size. Volumes are then allocated out of the storage pool and are mapped to a host system. 

MDisks can be added to a storage pool at any time to increase the capacity of the pool. MDisks can belong in only one storage pool. For more information, see Chapter 4, “Storage pools” on page 159. 

Each MDisk in the storage pool is divided into a number of extents. The size of the extent is selected by the administrator when the storage pool is created and cannot be changed later. The size of the extent ranges from 16 MB - 8 GB. 

Default extent size: The GUI of IBM Storwize V5000 Gen2 has a default extent size value of 1024 MB when you define a new storage pool. 

The extent size directly affects the maximum volume size and storage capacity of the clustered system. 

A system can manage 2^22 (4,194,304) extents. For example, with a 16 MB extent size, the system can manage up to 16 MB x 4,194,304 = 64 TB of storage. 

The effect of extent size on the maximum volume and cluster size is shown in Table 1-12. 

