Pros: Storage capacity is the ONLY good thing I have to say about this drive.

Cons: This drive unit continually drops connectivity from my system and displays I/O error banners. When encountering the I/O error, it also causes my computer's "System" process to run at around a 70-80% CPU usage level. I've searched both the Western Digital website's support and have found no acknowledgement of the issue. I've also loaded the latest firmware and WD utilities; still no resolution of the problem. I've found numerous Internet posts describing the same issues with no satisfactory resolution actions. The only way to keep this drive operating, is to periodically unplug and replug the power cord. This is unacceptable!

Other Thoughts: I own two other WD My Book drives (older models) and have had no issues with them. I also own a Buffalo TeraStation. I've had the TeraStation for over a year and have NEVER had a single issue with it. I considered getting a second Buffalo NAS, but chose the WD My Book instead--BIG MISTAKE! I now wish I'd gone with the Buffalo.

Hopefully someone from Western Digital will read this post and decide to do what's right--both acknowledge there's a problem and fix it.

Pros: What a device...12TB of storage, USB 3.0 expansion ports and hardware RAID. According to the specifications, the My Book Duo measures 6" x 6" x 4" and weighs in at a little over 5lbs, so this isn't something you'll be using on-the-go. It ships with two (2) 6TB WD Red drives designed specifically for NAS use. The WD Red drives have become some of the most reliable HDDs on the market recently, so it's nice to see WD using their flagship consumer grade HDD in this device.

The plastic lid pops off without the need for tools and provides access to the HDDs. Each drive can be removed from the back plane by pulling on a plastic tab (more on this tab later) and the drive slides out. This makes for a pretty quick drive change, except for having to transfer the posts from the old drive to the new drive.

Turn the device around and you'll find the Micro USB 3.0 PC interface, a power connection and a USB 3.0 hub containing 2 x USB 3.0 ports.

Out of the box, the device is configured for RAID 0 providing for a ton of storage buy no redundancy. I almost wish that WD would have shipped this RAID 1, as some people might not understand the different levels of RAID. I wouldn't want to see someone transfer all their files to the drive and later find out there was no drive failure protection. The RAID level can be changed by using the provided WD software.

Keep in mind that RAID 1 is not a viable backup. Partition tables can get hosed, power surges can destroy drives, you could knock it off the desk, etc. RAID 1 is only designed to protect against a mechanical HDD failure, it is not intended to be a sole solution for backup of data.

Speaking of software, WD provides their Utilities, Acronis True Image, WD Security and SmartWare. The Security software allows you to use the 256 bit AES encryption the device supports if you want to protect your data. Using a combination of the True Image and SmartWare, you can not only back up your data, but also image your machine. I would have liked to see both applications combined into one tool as opposed to having to use two separate programs for a complete backup.

With that said, the included software is easy to use and very straight forward.

Running some hardware transfer tests, I was seeing the following transfer rates:

RAID 1 - Write ~146MB/s
RAID 1 - Read ~161MB/s

RAID 0 - Write ~221MB/s
RAID 0 - Read - 252MB/s

Lets just say this is the fastest external HDD I've ever tested.

Cons: I was a little disappointed by the way the drives are removed. There is a cheap plastic tab that's attached to the post on the side of the drive and looks as though it could be easily ripped off the side of the drive. I would have preferred a latch system or some other way of removal. Other high end devices I've used allow drives to be swapped without the need for tools. I would have liked WD to include that as well. With their system, you still need a screwdriver to transfer the drive posts that align the drive when it's installed.

WD indicates that no tools are required to replace drives, but I'm still trying to figure out how that's possible since you definitely need a screw driver to transfer the posts on the sides of the drive. You can take a look at the NewEgg picture showing the top of the device open to see what I mean about the alignment posts.

Why the heck isn't there a LAN port on this thing? It just boggles my mind that you wouldn't include the ability to network this bad boy. I just can't think of anyone that would really need 12TB of local storage.

The warranty is a little too short for my liking. I would liked to have seen WD include a 5 year warranty on the My Book Duo.

My cons might seem petty, but I try to be overly thorough when I write my reviews. For these two reasons, I'm deducting 1 egg. If I had the ability, I would only deduct 1/2 egg, but NewEgg doesn't allow for 1/2 egg deductions.

Other Thoughts: The 12TB WD My Book Duo is fast, easy to install and comes with a great software suite. It is also affordable considering size and makes it easy for someone to add tons of storage to their local machine.

Even though I have a few small grips, it wouldn't keep me from recommending this to someone that needed additional local storage.

Pros: Easy setup.

Cons: None so far.

Other Thoughts: In the long run you'll never lose data if you decide to use the "Mirror" option.

Pros: Western Digital has a real winner on their hands with the My Book Duo 12TB. The external raid device has a wide range of flexibility. The My Book Duo offers the ability to set the RAID as either 0 (default out of the box), 1, or JBOD. Two Western Digital Red 6TB drives are inside providing the total 12TB of storage.

While being in RAID 0 on a USB3 port, read/write rates held steady between 270-285MBps. RAID 1 and JBOD, on the other hand, floated between 150-190MBps for both read and write speeds.

The addition of the two USB3 ports on the back of the unit, while sharing the bandwidth of the main USB3 back to the PC, afford the ability to plug items for either charging or light transfers. This proved especially helpful to charge a wireless headset.

Power saving is also a tremendous plus. The Duo will power down when the computer its connected to shuts down or goes to sleep. Many other external drives requiring external power will continue to run until they are manually turned off or unplugged.

Cons: These drives run hot. The ambient temperature around the unit for the majority of these tests remained around 70F(21C). After transferring data to the Duo for several hours, the drives began to alarm on my WHS due to temperatures of 127F (53C). Western Digital did not include any active cooling on the Duo choosing to, instead, rely thermodynamics to draw cool air through the vents in the bottom of the unit and expel hot air out of the top vents. For intermittent transfers, this works well but not prolonged periods. The specifications for the WD Red 6TB drives indicate this is within their operating temperature range of 32F(0C) to 158F(70C). Heat affects the longevity of all hard drives so this is a little concerning especially for an external hard drive RAID of this size.

Other Thoughts: I performed many of the prolonged tests by connecting the WD My Duo 12TB to WHSv1, FreeNAS, and Windows 8. With a little tweaking on the server side, WHSv1 recognized the entire 12TB and added was to the storage pool. In order to allow Drive Extender to perform correctly, the Duo was set to JBOD. FreeNAS and Windows 8 required minimal interaction in order to get the Duo to work in any of the three available RAIDs.

On a side note, I was able to control the heat issue by placing a USB powered fan on the top of the unit. By doing this, the temperatures came down to a more respectable 97F(36C). Again, the WD Reds can operate up to 158F according to Western Digital but this was for my own piece of mind.

Pros: It's exceedingly rare for me to ever give a glowing, two-thumbs up review on anything. But with this item, I pretty much have to.

Capacity--I received the 12-Terabyte model that came equipped with two six-Terabyte drives in RAID 0 configuration. That's pretty amazing, considering that the first hard drive I ever bought, back in the 1980s, had ten Megabytes of capacity, and was about the same physical size as this unit.

Linux Compatibility--I have no idea why Western Digital isn't advertising this. When I plugged this unit into my Lubuntu 13.10 machine, it was recognized immediately, and was automatically mounted under the "/media" directory. Lubuntu has the built-in capability of reading and writing to NTFS formatted drives, so there was no need to reformat the unit to use it with Linux. In fact, I now have backup files from the Linux machine peacefully co-existing with backup files from my Windows machines. (The only other Linux distro that I tried this with was Clonezilla, and it also worked perfectly.)

Speed--All of my Windows machines are so old that they all have the old USB 2.0 hubs. So, when I plugged the unit into them, I found that it was no faster than using a regular, cheap hard drive in a cheap enclosure. However, when I plugged the unit into my Lubuntu machine, the only one in the house that's new enough to have USB 3.0, I was blown away by the speed. When I did an "rsync" of a rather large directory, I was totally unprepared for how fast the operation would complete. (You need USB 3.0 to take advantage of RAID 0 write speeds.)

Backup Software Compatibility--The unit comes with its own backup software, but I also had it working perfectly with the backup utility that's built into Windows 7. As I type this, I'm using Clonezilla to create a backup image of a Windows XP drive on this unit. Clonezilla also recognized the unit immediately, and auto-mounted it as "/dev/sdb1".

Ease of Use--I've tried it with Windows Vista, Windows 7, and Lubuntu Linux. It's just an easy plug-and-play with all of them. (Note that if you plug it into a Windows XP machine, it will automatically install the drivers, but it still won't work. That's okay, because Western Digital doesn't advertise the 12-Terabyte model as being XP-compatible. Besides, there's still Clonezilla.)

Flexibility--The unit comes configured as RAID 0. However, you can easily change it to either RAID 1, or to use both drives independently

Cons: So far, none. Of course, I haven't had it long enough to evaluate the durability of the drives, but I have found in the past that Western Digital's warranty service is absolutely superb.

Other Thoughts: The software that comes with this unit is nice, and does have nice features. Once you install it on a Windows Vista, 7, or 8 computer, it will automatically backup your data files as you write them to the computer's hard drive. However, be aware that you can only install the software on one computer at a time. According to the owner's manual, if you want to install the software on another computer, you have to completely erase everything from the unit's drives, and then download a fresh copy of the software from the Western Digital site. However, installing the software on one computer does not prevent you from moving the unit to another computer, and using a different backup program.

For hard-drive backup, you can download the Acronis software for free. But, I found that it actually only gives the options to backup individual partitions, rather than the whoe drive. So, rather than use Acronis, I'll just stick to Clonezilla.