ok for my earlier question:

can i use NAS' USB to connect directly to a device like LCD TV?

i mean just like USB drive or those portable harddisks, where u hook them up and the TV will be able to read and play movie files.

Actually Synology DS213J only have 2 slots which means you can only do RAID 0 or 1. Forget about RAID 0 as it is the most risky setup.

You can use any HDDs for RAID 1 (mirrored) WD Green AV is a good candidate as wwgoh has pointed out esp if you will be torrenting from your box.

WD Red is useful when you are building RAID 5, 6 etc which will need 3 HDDs and above.

Guys, what is the normal RW speed for NAS (mine-netgear readyNAS 104 with 2x4TB WD red) connected to D-LINK DES 1016 D switch and with unifi 5mbps (i dont know if this is related)?

it seems i only get 8mbs max 

it could take days to transfer 1TB file 

Just change your switch, cheaper and less headache, for cheap layer-1 switch it's plug&play.
If you seriously needs 16-ports Gbps switch then it's much expensive, more than RM200+ (DLink brand), not so sure about TP-Link though.
8-port Gbps switch is around RM100 or less.
And about your "8mbps", is it MegaBytes? or Megabits? Huge difference there.

Cat5, erm... well Cat5e can sustain 1Gbps speed without any issue in my home's network, but I'm not so sure about huge office environment (more than 20 PCs).
For home network where there's less than 5 busy devices on a single network, it's fine to use just Cat5e with cheap layer-1 switch, no issue at all.
I'm using DLink 8-port Gbps switch, no issue on my end yet, been running months non-stop, the only bottleneck could be my hard disk, running without any RAID.
To maximize the huge files transfer speed in Windows network, you can actually set the Jumbo frame to 4K and above, but best to set a standard amount (4K or 8K, etc.) for all PC's network card for stability issue, it has been tested on my end here, from 60MB/s to 75MB/s, could be more depends on the hard disk speed again, can reach 90MB/s and above easily with really fast hard disk or SSD on both end.
For few PCs access a single device, that'll again depends on the hard disk accessibility speed, also it may depends on the services as well, priority queues stuff like that.
I have 2 PCs access a single file shares before, watching full HD movie on both sides without any issue, no lags at all, but if you going to seek the movie, probably will need to pause for few seconds (lag) instead of instantaneous seek.

Guys need some help, I am new to this NAS stuff.

My external USB HDD casing just died, HDD and data inside still ok.

I now like to find a new replacement HDD casing with below criteria:
1. Can be connect by wifi, which mean I can setup anywhere in my house as long as access to AC power socket and same wireless router; no need close to PC (by USB cable) or router (by LAN cable).
2. Usage: personal use storage, torrent, streaming 1080p video file thru wireless (local only, not internet)
3. Access from other places thru internet is a plus not a must, my screamyx upload is like shyte anyway.

Please recommend me a HDD housing that can fulfill the above criteria, thanks.
Let me know if I am posting in wrong topic.

What size you buy?

I have a 6tb used. But I forget what is the condition.