single vs dual fabric

Dual Fabrics

For mission critical applications, Brocade strongly recommends that you install a dual fabric, which allows you to upgrade each fabric separately with no loss of service (provided that you have configured failover software).
For example, to upgrade the dual fabric shown in the picture, you first upgrade Fabric 1 by deactivating the link from the host to Fabric 1. The host continues to access the data through Fabric

2. After Fabric 1 is upgraded, reconnect the host to Fabric 1, disconnect the link from the host to Fabric 2, and upgrade Fabric 2.