I have an old iomega with a gigabyte connection but it only transfers at about 12mb per second... I only need a 2 TB NAS but would like to be able to write to it at about 200mb per second. Why incorporate a 1GB NIC in the NAS if it is only going to run at 12mb???????? Crazy crap... My pc's are all high end, have 1GB NIC's and my linksys switch is also 1GB....
Basically you have an older "NAS" that is only transferring at 12MB or 12Mb per second?
12MB sounds like a 100Mbps network adapter inside it and your limited by that speed.
You won't get 2TB @ 200MB/s without some expensive SSD's or a high end server RAID card with 5~7 disks. The limit of a 1Gbps connection is 100MBps anyway. Most platter HDD's have 40MBps average sustained read speed with bursts going up to 60~65.
A 1GB NIC in the NAS is only 1/3 the equation. Obviously your PC must have a 1 GB NIC also, but you also must be using a 1GB SWITCH (many routers only have 10/100 capability if they are a few years old.
Further, ReadyNAS and many other NAS have the option of "Jumbo Frames" which is typically off by default; you could test that option.
12MB/s is the max you can push through a 100/t connection. If you upgrade to 1000/t (or Gigabit Ethernet) then you will have a max of 120MB/s. 100megabits/8bits to a byte = 12 Megabytes per sec, similarly 1000megabits/8bits to a byte is 120Megabytes per sec. And Fiber or 10,000megabits/8bits per byte comes to 1.2GB/s, but that isnt really for home use yet Plus there is traffic on the network, and overhead for the transfer protocoll, so you never really get the max through the network, but you should be able to get a solid 115MB/s if everything is set up correctly.
You will need 1000/t on each computer (default on most computers made in the last 6-7 years), you will need a 1000/t router or switch, and you will need either modern HDDs, an SSD, or a RAID array (on both ends for both reading and writing) to push the data fast enough to max out the bandwidth. Also, if you are more than ~30ft away from a device then you may need CAT6 wire instead of CAT5 or CAT5e (your mileage will varry, I have cheap CAT5 in my house, and only one computer refuses to connect at 1000/t). If you have a NAS I highly suggest RAID 1, 10, or 5 (5 is a bit slow and harder to manage than the others), so that if you have a drive fail on your NAS then you will be able to recover the data that was lost. Also it will help throughput if you have multiple users pulling information at the same time. For an OS I suggest FreeNAS if you are not afraid of Linux, or Windows Home Server which is bone-head easy to set up and use.