Hello,

You can replace the 1TB drives one at a time, and then extend the array through OpenManage. This is how I would recommend doing it.

I didn't follow your original post at all, so I'm not sure if you were suggesting an option or simply asking for one, but you can:

1. Backup and restore to a larger array
2. Set up new/second array and clone from one array to another
3. Do as Dylan suggested, rebuild each one at a time, then rebuild/extend the array to fill the space

Yeah, that was NOT clear from your original post.

Yes, you can add two new drives in a second RAID 1.

"extend disk 0 with the new configure raid 1 drive"

Still unsure what you mean by this … if you add drives in a second RAID 1, then leave them in a RAID 1 as a separate "disk" in the OS. Do NOT attempt to "span" the two disks to create one volume.

by "extend", I mean using the windows Disk management and Extend volume

Ah, I see … totally fine.

You can extend C:, so long as it is the last (right-most) partition on the disk and the disk is 1) less than 2TB (ending size) OR 2) GPT disk installed in UEFI-enabled system.

If it is the C volume, I do not believe Windows will allow the operation. If it is not the C volume, you may be able to extend to another volume. 

Most expansions I've assisted with were to grow the RAID from the hardware level, then extend the storage into it.