Testing harddrive performance by inserting them into a Synology NAS is just a joke !!!!
Synology IO performance is HORRIBLE compared to any decent hardware !
in my computer i had 3x WD30EZRX (WD 3 TB Green) in RAID 0 and could read/write at 400/350 MB/s
Raid 5 performance was 350/250 MB/s
Hardware : Core i5 4570, ASUS H87i-PLUS (Intel Raid controller)
on the other hand, running a virtual Synology DSM 4.3 (XPenology) i didn't get the same performance from the same disks. I didn't do a thourough benchmark but the initial speeds was only about 100 MB/s read/write. i'll do a test once i get new disks (WD Green was returned)