Japanese user's guide for the Sonnet Fusion R400QR5 4-drive RAID 5 SATA storage system with quad interface. These directions apply to storage systems with drives.
Yes you can. Your array will use 4x the capacity of the smallest capacity drive. For example, If you install one 1TB drive and three 2TB drives, then the D/R400QR5 will build a 4TB RAID0 (4x 1TB) or a 3TB RAID 5 (3x1TB + 1TB parity). The extra capacity will go unused.