Hello Gunners777,   It is always recommended to create a validated backup of your data before starting any action.   A RAID1 is only two drives, you cannot add more drives to this RAID level.   You could add the drives and do a Raid Level Migration  on RAID1 to RAID5 or RAID6 See table on this link Source and Target level :  [URL]   The document you have is good and this video may help. Performing Online Capacity Expansion on PERC controller [URL]   If you want to maintain a mirrored array then you would backup, delete VD, create RAID10 with all the drives and restore from backup.  
HI All, I have a Raid1 vdisk with 2 drives, currently running HyperV with critical workloads. Need more capacity on the volume, purchased 2 additional drives. Found this link [URL] Worried that if i do incorrectly will lose data for the customer, Is this procedure correct any advice please. Also is point 6 the correct option?"reconfigure virtual disks"   Thank you All!
Add disk to existing Raid1