First decide whether you want to simply create a new Cluster Shared Volume or extend the old one. If you decide to create a new one and want to move VMs there you can using Storage Migration but there will be downtime!
Steps to extend existing CSV:
- Login to SAN management, go to the lun or disk and increase its total volume
- Open the Microsoft Failover Cluster Manager and check the CSV coordinator for the disk or LUN you expanded. (the coordinator is the disk owner for the cluster)
- GUI Version:
- Use Disk Management under STORAGE under the Server Manager. Rescan for disks and expand the disk or lun to the new capacity.
- For Hyper-V or Windows Server Core, you can use DiskPart
- list volume
- select volume <vol # to extend>
- list volume to check the new volume size