All Oracle ASM installations can be configured to serve Oracle ASM Flex Clients.
On the left, Server 1 is the traditional Standalone configuration with the ASM instance local to the database instance. In the past this was the only configuration available. Each node had to have an Oracle ASM instance, if Oracle ASM was used to provide shared storage.
Notice that Server 2, is an Oracle ASM client node. It uses the Oracle ASM service on Server 3, another node in the cluster, to access the metadata, and then does direct access to Oracle ASM disk storage for the data blocks.
To the right, is Server 5. It has no direct access to the Oracle ASM disk storage, but gets all the data through the IO Server (IOS) on Server 4. The Oracle IO Server was introduced in Oracle Grid Infrastructure version 12.2. IOS enables you to configure client clusters on such nodes. On the storage cluster, clients send their IO requests to network ports opened by an IOServer. The IOServer instance receives data packets from the client and performs the appropriate IO to Oracle ASM disks similar to any other database client. On the client side, databases can use dNFS to communicate with an IOServer instance. However, there is no client side configuration so you are not required to provide a server IP address or any additional configuration information. On servers and clusters that are configured to access Oracle ASM files through IOServer, the discovery of the Oracle IOS instance occurs automatically.
Each Oracle ASM instance in a cluster has access to the Oracle ASM disk storage in that cluster. Oracle ASM disks are shared disks attached to the nodes of the cluster, in possibly varying ways, as shown in the graphic. Oracle ASM manages Disk Groups rather than individual disks. The Oracle ASM utilities allow you to add disks, partitions, logical volumes or Network attached files (NFS) to a disk group.