4 hours to copy a 138 MB folder? Hmm, something is clearly very wrong with this setup - this is not representative of the speed you should expect from your 412+. By that I mean it should be around 5000x faster - copying 140 ish MB to my 1812+ takes approximately 2 seconds.
I would follow up with Synology support to determine exactly what the problem is. It might be something wrong with your particular unit, but considering you have two of them (and they are both equally slow?) ... there might be some other cause, possibly related to setup and configuration. Good luck with it, hopefully Synology support can help you it.
But again, these devices are designed to be a lot faster than this..
DS1812+ 4 x 3 TB Seagate Barracuda (SHR), 2 x 2 TB Western Digital (RAID 1), DSM 4.0
27" iMac 16 GB RAM, 3 TB Fusion Drive, NVidia GTX 680 2 GB, OS X 10.8 Mountain Lion
Mac Pro 6 GB RAM, 120 GB Intel SSD, 1.5 TB Western Digital, ATI Radeon 5770 1 GB, OS X 10.8 Mountain Lion Server
Mac mini 8 GB RAM, 2 x 500 GB HDD, OS X 10.8 Mountain Lion Server