Switch to the Grid user, and run the ASMCA command to create a disk group:
[grid@rac-node01 grid_home]$ asmca -silent -creatediskgroup -diskgroupname DATA -disklist '/dev/vdf,/dev/vdg,/dev/vdh' -redundancy EXTERNAL
After the disk group is created, you can see the new disk group in the cluster status:
[grid@rac-node01 grid_home]$ crsctl stat res -t...ora.DATA.dg(ora.asmgroup) 1 ONLINE ONLINE rac-node01 STABLE 2 ONLINE ONLINE rac-node02 STABLE 3 ONLINE OFFLINE STABLE...
Adding New Disk to DATA DG
To add a new disk to the ASM disk group, run the following command (you may need to run the command twice):
asmca -silent -addDisk -diskGroupName DATA -disk '/dev/vdi'