Question 1

Are there any restrictions on size or specs of 3.5" HDDs I can use with this unit? I have a pair of 3.5" 6TB Western Digital Red hard drives. Can I use them?

Accepted Answer

According to the Synology website, the maximum single volume size varies with CPU architecture. As for the DS218+, DS218, DS218play, the maximum single volume is 108TB. The DS218j, having a 32-bit CPU is limited to 16TB single volume size. 
So, assuming you have a DS218 (64-bit CPU), you would be limited to a single volume size of 108TB or less. Since the DS218 is a two disk solution, that implies each disk must be less than 54TB. Would your two 6TB disks work? Pretty sure. (FYI: I have two 4TB WD Red's in my DS218.)

Question 2

Is this the same as the DS218+ model?

Accepted Answer

The direct answer is 'NO'. But for the best comparison, use Newegg's 'Compare' feature on the two models. In the DS218 model line, the '+' version is supposed to be the highest performer. It does feature a dual-core Intel Celeron vs. a Realtek quad core processor. Memory is expandable, which is a plus. Of course, you must pay a bit more for this slightly higher performance and expandability. The DS218 is fine for lower cost home use. The DS218+ is better for an 'advanced' home user or even a (very) small office.

Question 3

Synology 2 bay NAS DiskStation DS218 (Diskless) - OEM    What does "OEM" imply?

Accepted Answer

OEM is an acronym meaning Original Equipment Manufacture. It's normally applied to products that might be used by equipment manufacturers. But in this case, I think it refers to the fact that SYNOLOGY is itself an OEM and produces the product advertised, as opposed to just a re-seller. I own a DS218. It's a very nice NAS device. Good value proposition.

Question 4

can it work using a usb or ehternet cable when connecting to a modem?

Accepted Answer

yes

Question 5

does oem come with a power cord?

Accepted Answer

Mine did

Question 6

Are there any limitations on the size or specs of HDDs I can use with this unit? I have a pair of 6TB WD Red 3.5" drives. Can I use them?

Accepted Answer

Looks like it can. Synology has a compatibility chart that I tried to link, but newegg wont let me.

Questions & Answers