Yes, that is usually done via hard drive or partition level backup. One of the tools you might have or stop your eye on: Paragon Drive Backup 10 Server:
www.drive-backup.comSymantec Ghost:
www.symantec.comAcronis True Image:
www.acronis.comHow it would look with Drive Backup 10 (I use it personally):
a)Download and install program - Run Backup wizard - create image to external drive or network share.
b)Shut down the server and replace the small drives with bigger ones. Rebuild RAID1 with new drives via RAID utility.
c)Boot the server from WinPE Recovery CD for Drive Backup - load drivers for RAID if needed for better HDD detection.
d)Run Drive Backup 10 from WinPE and restore from backup. During restore you can resize the partitions proportionally so the new space would be allocated to existing partitions automatically. Apply changes and wait till the end of operation. Restart to Windows.
Done.
If you have more than one DC in your network then save System State backup via NTbackup before running any of the mentioned backup software.