You cannot "expand" the array in the way you have tried to do. The only way to expand a Virtual Disk is to Reconfigure the array by adding a disk. For example, you can reconfigure from a 3-disk RAID 5 to a 4-disk RAID 5, or a 4-disk RAID 10 to a 6-disk RAID 10. Similarly, you can reconfigure your 2-disk RAID 1 to a 2-disk RAID 0 or to a 3-disk RAID 5.
At this point, having replaced each individual drive within the array, you have two choices: 1) Create a second array across the disks utilizing the available space on the drives, 2) backup data, delete array, create array of desired size with larger disks, restore.
There is another option, called a retag that you might hear or read about, but it should only be used if this is a matter of convenience and you don't care about the data on the array or have very good, effective backups and don't mind restoring from backup when the array fails. The retag is a recovery tool and was never intended to be used to "expand" the array using larger disks - that is a side-effect of the retag. The reason you should not use it is it creates a unstable array and it becomes only a matter of time before the array suffers catastrophic failure.
