Thanks rjc, this is exactly the answer I got from Synology. Actually the software encryption on the DS412+ gives better results than the hardware encryption on the DS212+, due to the powerful CPU on the DS412+.
AES 256-bit Encrypted File Upload/Download(1) (5GB File)
22.65MB/sec upload and 31.69 MB/sec download for the DS412+ (soft encryption)
13.20MB/sec upload and 23.46 MB/sec download for the DS212+ (hard encryption)
The procedure to activate the encryption is described here:http://www.synology.com/tutorials/how_t ... p?lang=enu